A zoological garden, shortened to zoo, is an institution in which living animals are exhibited in captivity. In addition to their status as tourist attractions and recreational facilities, modern zoos may engage in captive breeding programs, conservation study, and educational outreach. Zoos are a subject of controversy stemming from many sources, including the quality of life of the animals they exhibit, and the perceived necessity or purpose of exhibiting captive animals at all. Zoos are frequently criticized by animal rights groups. 
Collections of wild animals existed already in the ancient civilizations of Mesopotamia, Egypt, and China. In medieval Europe some monarchs, monasteries, and municipalities continued to maintain collections of wild animals. The transition from menagerie, a predominantly private collection, to public institution marks the beginning of the modern zoo concept. Collections established during the nineteenth century began calling themselves zoological gardens. Throughout the nineteenth and twentieth centuries, many new zoos and related facilities were founded for very different motives and purposes.
Zoo professionals proclaim demanding aims for their institutions, from educating the public to conservation of biodiversity. Many zoos define their aims as recreation, education, research, and conservation. Animal-rights groups claim that there is a wide gap between these claimed aims and actual practice, and that zoos have commercial and entertainment purposes in mind as well as financial profit.
Types of zoo include urban, open-range, safari, animal theme, roadside, rescue, sanctuary, petting, and specialized. The most traditional form of maintaining wild animals in captivity is keeping them in cages constructed of concrete or metal, in aviaries, or fenced paddocks. Most zoological gardens incorporated within international umbrella organizations are led by professionals such as zoologists or veterinarians.
The terms zoo and zoological garden, that refer to zoology (from Greek: zωο, zoion, "animal"; and λόγος, logos, "knowledge"), did not come into use until the modern zoo concept developed during the nineteenth century. The Zoological Society of London first used this term to describe its collection at Regent's Park, although this collection was simultaneously referred to as a menagerie. Most zoo founders of the nineteenth century operated with the term zoological garden to distinguish their institutions from the aristocratic and travelling menageries. The abbreviation zoo first appeared in Britain about 1847, when it was used for the Clifton Zoo, but it was not until some twenty years later that the shortened form became popular by a song called "Walking in the Zoo on Sunday". Relatively new terms for zoos, which were coined in the late twentieth century, are conservation park or biopark. Adopting a new name is a strategy by some zoo professionals to distance their institutions from the stereotypical and nowadays criticized zoo concept of the nineteenth century.
 From ancient to modern times
Collections of wild animals existed already in the ancient civilizations of Mesopotamia, Egypt, and China.
The most abundant evidence of the earliest zoos from Egypt derives from burial sites of about 2500 BC to 1400 BC. Throughout the entire period, written records -- on tablets, papyri, and tomb walls -- describe how pharaohs and sometimes other power brokers made zoos for pleasure and prestige and to satisfy scientific curiosity. Rulers gathered many of their animals from distant lands, frequently setting forth on expeditions for that purpose or receiving their quarry as gifts from fellow leaders or conquered peoples. Proud of their collections, they took pains to ensure that their acquisitions would thrive and reproduce. Indeed, they often employed handlers to care for finicky creatures.  The ancient Egyptians began keeping wild animals in form of acclimatization which sometimes has approached domestication. On tomb pictures dating from 2500 BC, at Saqqara, some ungulates including antelopes, gazelles and ibex are depicted wearing collars and holding in leash. Egyptian Queen Hatshepsut established a zoo in Thebes around 1490 BC. Hatshepsut's zoo contained exotic animals collected from what is today Somalia, and it included cheetahs, leopards, monkeys and a giraffe.
In ancient China, wild animals, especially exotic species, held the interest of rulers and the wealthy class. Starting with the founder of the Shang dynasty (ca. 1500 BC), China's rulers built animal reserves. However, it was Wen Wang, founder of the Zhou dynasty (ca. 1000-200 BC), who built the first well-known animal reserve, which he called Lingyou, commonly referred to as the "Garden of Intelligence". A more accurate translation would be "Garden for the Encouragement of Knowledge". This reserve and similar parks owned by the wealthy class of the Zhou period were large, walled-in natural areas that required their own staffs of administrators, keepers, and veterinarians. The rulers of the Qin, Han, Tang, and Song dynasties continued the fashion of large royal parks, where birds and mammals were kept in cages for personal pleasure and the demonstration of wealth and power.
Also in the ancient Greek and Roman world live animal collections existed. Historians have written many publications about extravagant and bloodthirsty spectacles in Rome, involving wild animals. The 19th-century historian W.E.H. Lecky wrote of the Roman games, first held in 366 BC: "At one time, a bear and a bull, chained together, rolled in fierce contest along the sand ... Four hundred bears were killed in a single day under Caligula ... Under Nero, four hundred tigers fought with bulls and elephants. In a single day, at the dedication of the Colosseum by Titus, five thousand animals perished. Under Trajan ... lions, tigers, elephants, rhinoceroses, hippopotami, giraffes, bulls, stags, even crocodiles and serpents were employed to give novelty to the spectacle ..."  However, little has been written about the facilities of keeping those animals. The Latin word vivarium referred to the stockyards and arenas where wild animals were held for public spectacles.
In medieval Europe some monarchs, monasteries, and municipalities continued to maintain collections of wild animals. One of these collections was the Tower Menagerie in London.
In the New World, one of the earliest and most impressive collections of animals was that of the Aztec emperor Montezuma II in Tenochtitlan (now Mexico City). It contained several buildings and flight cages and numerous gardens, lakes, streams, and ponds for its birds, mammals and reptiles. Hundred of gardeners and animals keepers tended the collections and the grounds. Unfortunately, these animal collections were destroyed during the Spanish conquest (1519-1521) by Hernando Cortés. 
At the middle of the 16th century, Hessen was ruled by Landgraf Wilhelm IV. In 1571 this prince established a zoological garden at the Sababurg, the hunting castle in the heart of the Reinhards Forest not far from Kassel. The prime purpose of the wild animal park was at first to furnish the kitchens with meat. 
Menageries owned by monarchs and wealthy aristocrats can be seen as the predecessor institution of the modern zoological garden. One of these aristocratic menageries was the Versailles menagerie during the reign of Louis XIV. The oldest existing zoo, the Tiergarten Schönbrunn in Vienna, evolved from such an aristocratic menagerie, founded by the Habsburg monarchy in 1752.
 Evolution of the modern zoo concept
The transition from menagerie, a predominantly private collection, to public institution marks the beginning of the modern zoo concept. Collections established during the nineteenth century began calling themselves zoological gardens. In some cases this was simply fashionable since zoos were considered professionally managed facilities, whether they were or not. In other cases there was an emphasis on education and science rather than on entertainment. The first modern zoo, established particularly for scientific and educational purposes according to its founders, was the Ménagerie du Jardin des Plantes as part of the Muséum national d'histoire naturelle in Paris (1793). It was, significantly, laid out like a picturesque park -- a semblance of Nature emphasized by Rousseau -- while the buildings themselves housed caged animals as if in museum display cabinets.  About thirty years later, the members of the Zoological Society of London adopted the idea of the early Paris zoo when they established London Zoo in 1827. It opened in 1828 in Regent's Park, admitting members and their guests. Only in 1847 were working people allowed in, for a shilling. The taxonomic presentation of animals at the London Zoo became the model for the nineteenth century. The success of London Zoo set off a Victorian wave of similar establishments. 
The world’s first acclimatization society was the Société Zoologique d’Acclimatation, founded in Paris in 1854.  The founding president was Isidore Geoffroy Saint-Hilaire, professor of zoology at the Muséum national d'histoire naturelle and director of the Ménagerie (created in 1793). In 1860 Isidore and his son, Albert Geoffroy Saint-Hilaire, opened Jardin Zoologique d’Acclimatation, located in the Bois de Boulogne, west of Paris. 
In the United States, physician William Camac initiated the incorporation of the Zoological Society of Philadelphia in 1859. According to the society's charter, "The object of this Corporation shall be the purchase and collection of living wild and other animals, for the purpose of public exhibition at some suitable place in the City of Philadelphia, for the instruction and recreation of the people." The American Civil War interrupted these efforts so that the opening of the Philadelphia Zoo delayed until 1874. Some years ago, the Central Park menagerie evolved from gifts of exotic pets and other animals informally given to the Park, beginning, apparently, with a bear and some swans deposited near New York's arsenal on the edge of Central Park in 1859. About 1861/62, a smaller zoo with lower standards had been already established in New York City, the Central Park Zoo. In 1864 it received charter confirmation from New York's assembly. When the first American zoological gardens came into existence, only a few supporters of the early animal welfare movement spoke out against zoos. Humanitarians protested cruelty in training animals for circuses more often than they opposed zoos. Their concerns were that zoo animals were healthy and well cared for, and not subjected to cruelty or pain.
In March 1889 an Act of Congress authorized the formation of a National Zoological Park Commission to select an purchase land for a zoological park in the District of Columbia "for the advancement of science and the instruction and recreation of the people". In April 1890 Congress passed another act, placing the National Zoological Park under the direction of the Smithsonian Institution's Board of Regents. 
Throughout the nineteenth and twentieth centuries, many new zoos and related facilities were founded for very different motives and purposes. Cultural and philosophical attitudes as well as political developments such as imperialism had an impact on the appearance and aims of zoological gardens. Human beings were sometimes displayed in zoos along with non-human animals, supposedly to illustrate the differences between people of European and non-European origin (“Human zoos”). According to historians Eric Baratay and Elisabeth Hardouin-Fugier the zoos of that period reflected the determination of imperialist nations to classify and dominate.
In 1931, a small zoo was built by the Hagenbeck's firm for the Colonial Exposition organized by Lyautey in Paris.  The popular success of this temporary zoo inspired the Muséum national d'histoire naturelle to create a new zoological garden inaugurated in 1934 in the Bois de Vincennes, east of Paris. 
In the 1950s, Bernhard Grzimek used the zoo and the zoological society of Frankfurt to popularize the idea of nature conservation.  When ecology emerged as a matter of public interest through the 1970s, a few zoos began to consider making conservation their central role, with Gerald Durrell of Jersey Zoo, George Rabb of Brookfield Zoo, and William Conway of Bronx Zoo leading the discussion.  Since then, zoo professionals became increasingly aware of the need to engage themselves in conservation. Especially in America, the new zoo concept had been developed.  The changes at zoos have served both the ideology of environmentalism and the day-to-day needs of zoos to maintain their collections. Many of contemporary zoos led by professionals show fewer species and display social animals in groups; landscape immersion exhibits replicate animal habitats.
- Further information: List of zoos
Zoo professionals proclaim exalting and demanding aims for their institutions, from educating the public to conservation of biodiversity.  Many zoos define their aims as recreation, education, research, and conservation. Animal-rights groups claim that there is a wide gap between the claimed aims and actual practice, and that owners of zoos have commercial and entertainment purposes in mind to increase their financial profit. Some zoos work to save endangered species, but most animals in zoos are bred in captivity for the purpose of public display, not species protection. In his 1985 critique of zoos, philosopher Dale Jamieson asserted that zoos generally do not live up to their own goals, that zoo animals are deprived of freedom for little social or scientific good, and that zoos cause suffering without producing compensatory benefits for animals or people. Jamieson argues that a moral presumption against keeping animals in captivity outweighs any benefit that might accrue from education, science, or species preservation. The animal rights philosophy refuses zoos as a matter of principle. Keeping wild animals in captivity is seen as human domination over other creatures.
French historians Baratay and Hardouin-Fugier see zoos as an allegory for the contradictions of modern Western societies: "The zoo made concrete, in an enclosed space, what society wanted to do in nature, as, with the advance of urbanization, people felt an increasing need to preserve the wild. But the desire remained unrealized, because Western society did not want its methods called into question, and because, in the final analysis, it preferred to transplant, delimit, cultivate and arrange nature however and wherever it liked, rather than leave places truly free of human influence."
Recreation, which is close to entertainment and pleasure, does not benefit the welfare of the zoo animals, but that of the zoo visitors. Jamieson points out that "we should have the honesty to recognize that zoos are for us rather than for the animals". According to Swiss zoologist Heini Hediger recreation is one of the most important aims of the modern zoo in the face of proceeding urbanization and alienation from nature. People, especially from urbanized areas, should be given the opportunity to relax and to enjoy a naturalistic environment in their very neighbourhood.
Since the beginning of the modern zoological gardens education and therefore the propagation of biological knowledge has been one of the most prominent aims claimed by zoo professionals. Already in 1829, London Zoo published its first guide to the zoo. Today’s educational efforts of zoos concentrate mostly on ecological and conservation issues. The idea of conservation education at zoos has a longer history than it is often acknowledged. This idea was foremost among the goals of the Arizona-Sonora Desert Museum as it was planned in the early 1950s. Animal exhibits were one component of the museum, which was begun with the goal of educating the public about the plant life and scenic value of the desert. Although the museum's focus was regional, and it was not a traditional zoo, directors of many American zoos looked to it as a model. Many zoos now have an education department, a classroom, and full time educational officers. Edinburgh Zoo has pioneered a scheme called "interlink" which combines the resources of the zoo, local museums, and the botanical gardens to create educational courses. Like several other zoos it offers teachers a range of courses from day trips with infants to intensive courses for advanced students. In 1991, over 50,000 students were involved with structured courses at Edinburgh Zoo. However, critics say that there is no educational value in exhibiting wild animals in artificial environments. According to them true respect for wildlife could only be stimulated by learning about animals in their natural habitat.
Classical zoological gardens played a role in research in comparative anatomy and physiology in the nineteenth century. Important scientists, such as Cuvier, Alfred Brehm and Paul Matschie, used zoos for their studies. 
Heini Hediger developped zoo biology as a special branch of biology. Zoo biology translates the ideas and perceptions of others sciences into the practice of zoological garden management and gives stimulus to the use of zoo research in other sciences. 
Contemporary research efforts focus on ethology and conservation breeding. According to William Conway zoo science would contribute basic biological information and technological know-how to the increasingly demanding tasks of wildlife care in constricted habitats.
Up to now, only a few species such as the Przewalski’s Horse, the American Bison, or the California Condor could be saved from extinction and reintroduced to the wild. The American Bison, for example, was close to extinction at the beginning of the twentieth century. In 1907, the Bronx Zoo led by William T. Hornaday was the first zoo to help the American Bison Society with its reintroduction project, sending 15 bison to the Wichita Forest Reserve in Oklahoma. Other reservation herds were established in succeeding years using additional zoo-bred animals. By 1933, there were 4,404 bison in the United States and 17,043 in Canada.  Although most species maintained in zoos are not endangered, and those that are will likely seldom be released into natural habitats, biologist Colin Tudge emphasizes the urgency of ex-situ conservation in zoos in the face of increasing threat to natural habitats.
In 1993, the World Association of Zoos and Aquariums (WAZA), formerly known as the International Union of the Directors of Zoological Gardens, produced its first conservation strategy. In November 2004, WAZA adopted a new strategy that sets out the aims and mission of zoological gardens of the twenty-first century. The captive breeding of endangered species is coordinated by cooperative breeding programs. Under the auspices of WAZA, 182 International Studbooks are kept. These studbooks are coordinated by the Zoological Society of London. About 810 animal species and subspecies are managed under cooperative breeding programmes at the level of the regional association members such as the Species Survival Plan (SSP), established 1981, or the European Endangered Species Programme (EEP), established 1985.
But critics point to the marginal contribution of zoos to the preservation of biodiversity. Andrew Linzey, director of the Oxford Centre for Animal Ethics, argues that zoos make a "minuscule contribution to conservation." Most conservation experts agree that few of the rare or endangered species can be saved from extinction by breeding them in captivity. In 1990, the International Union for the Conservation of Nature (IUCN) drew up an action plan for the survival of 1370 species. It considered that the reintroduction of captive bred animals could assist in the conservation of only 19 species (1.4 percent). The difficulties associated with ex-situ conservation are illustrated by the captive breeding program for the critically endangered Sumatran rhinoceros. Between 1984 and 1996, 40 Sumatran Rhinos were transported from their native habitat to zoos and reserves across the world. After years of failed attempts and a dramatic decline of the captive population, one individual gave birth to a healthy male calf at Cincinnati Zoo in September 2001. This was the first successful captive birth of a Sumatran Rhino in 112 years. Two other calves followed in 2004 and 2007. Despite the recent successes in Cincinnati, the captive breeding program has remained controversial. Proponents argue that zoos have aided the conservation effort by studying the reproductive habits, raising public awareness and education about the rhinos, and helping raise financial resources for conservation efforts in Sumatra. Opponents of the captive breeding program argue that losses are too great; the program too expensive; removing rhinos from their habitat, even temporarily, alters their ecological role; and captive populations cannot match the rate of recovery seen in well-protected native habitats.
 Urban zoos
Urban zoos are the classical zoological gardens that stand in the tradition of the nineteenth century zoo concept, even if some of them changed their names to Conservation Park or Biopark. Most of them are relatively small in size and based within cities or urbanized areas, a fact that often complicates the construction of more sizable enclosures. In Europe a famous urban zoo is the Antwerp Zoo in Belgium, right next to the central station of the city. In the USA a good example is the Cincinnati Zoo.
 Open-range zoos
A number of open-range zoos have been established since the early 1930s in rural surroundings. The prototype is Whipsnade Park, England, established by the Zoological Society of London in 1932 (600 acres, 2.4 km²). Fewer species are exhibited in such zoos than in urban zoos, but they are mostly kept in more sizable enclosures. The largest zoo in terms of size is the 1,800 acre (7 km²) San Diego Wild Animal Park in the Pasqual Valley, California, that is run by the Zoological Society of San Diego. The Werribee Open Range Zoo near Melbourne, Australia, concentrates on displaying animals living in a wide open savanna. This 500-acre (2.0 km2) zoo is managed by the Zoological Parks and Gardens Board which also manages Melbourne Zoo. One of only two American state supported zoos is the 535-acre (2.17 km2) North Carolina Zoo located in Asheboro, North Carolina.
 Safari parks
A safari park is a zoo-like commercial tourist attraction where visitors can drive in their own vehicles and observe the wildlife, rather than viewing animals in cages or small enclosures. Most safari parks were established in a short period of ten years, between 1966 and 1975.
 Animal theme parks
An animal theme park is a combination of an amusement park and a zoo, mainly for entertaining and commercial purposes. Marine mammal parks such as Sea World and Marineland are more elaborate dolphinariums keeping whales, and containing additional entertainment attractions.
Another kind of animal theme park is Disney's Animal Kingdom in Orlando, Florida (550 acres, 2.2 km²) or Busch Gardens Africa in Tampa, Florida (335 acres, 1.34 km²). These commercial parks are similar to open-range zoos according to size, but different in intention and appearance since they contain far more entertainment elements (stage shows, roller coasters, mythical creatures etc.).
 Roadside zoos
There are hundreds of substandard wildlife attractions throughout the United States and Canada called roadside zoos. These mainly amateur facilities are usually privately owned and occasionally accredited by the American zoo organization AZA. The focus is on amusing customers, rather than on meeting the needs of the animals. Roadside zoos often lack trained, experienced animal care staff, proper funding and safety practices. Animals are confined to small, barren, often filthy cages, and suffer poor welfare as a result of inadequate housing, care and diet. Roadside zoos breed animals in order to have a constant supply of cute babies to attract the public. Big cat rescues, primate rescues, and native wildlife rescues are overwhelmed due to the constant influx of animals coming out of roadside zoos.
 Rescues and sanctuaries
Animal welfare supporters have funded the construction and set-up of sanctuaries for wild animals. The animal welfare organization WSPA established several of these facilities for rescued bears worldwide. According to the organization those in Greece and Turkey have helped stamp out the tradition of forcing bears to perform tricks for public entertainment. Another type of sanctuary takes the form of a rehabilitation and release center. An example of this is the Idaho Black Bear Rehabilitation Center, where orphaned bear cubs are cared for and prepared for release back into the wild. Another sanctuary, especially for apes and primates, is 65 acre (0.26 km²) Monkey World near Wool, Dorset, England. Set up in 1987 it was originally intended to provide a home for abused chimpanzees used by Spanish beach photographers, but is now home to many different species of primates.
 Petting zoos
A petting zoo, also called children's farms or children's zoos, features a combination of domestic animals and wild species that are docile enough to touch and feed. To ensure the animals' health, the food is supplied by the zoo, either from vending machines or a kiosk nearby.
 Specialized zoos
 Traditional enclosures and new approaches
The most traditional form of maintaining wild animals in captivity is keeping them in pits (“bear pits”), in cages constructed of metal bars or concrete, in aviaries, or fenced paddocks, although many zoos replaced these by more elaborate and larger enclosures that attempt to replicate their natural habitats, for the benefit of the animals and the visitors. 
In the zoological gardens of European cities, are all those structures in exotic styles which, in the nineteenth century, were thought appropriate as the home of wild creatures from foreign parts: the Egyptian temple in Antwerp Zoo (1856), the Moorish-looking elephant house at the Cologne Zoo (1863), the Indian pagoda for elephants in Berlin Zoo (1873), the Turkish elephant house at Basel (1891). 
The first exotic design for a zoo building was the Egyptian temple at the Antwerp Zoo.  Antwerp's Egyptian temple was a faithful reproduction of an ancient temple on the Isle of Philae.  It was built for elephants, giraffes and zebras, in 1856. Its architect, Charles Servais, used the Egyptian style for all kinds of African animals. 
German merchant Carl Hagenbeck developed a new form of animal exhibition at the beginning of the twentieth century. When he opened his private owned zoo at Stellingen near Hamburg, (Tierpark Hagenbeck) in 1907, Hagenbeck had broken with a strong tradition to exhibit animals in accordance with taxonomy. He created a new style of exhibition based on ecological and geographical habitats including different species. For example, the "Northern Panorama" exhibited seals and walruses in a pool in the foreground, with reindeer behind them, and polar bears behind the reindeer. In the "African Panorama", the foreground pond had ducks and flamingos; behind them were large plains with zebras, antelopes, and ostriches; behind them were lions and vultures at the foot of an artificial mountain, on which were ibex or barbary sheep. The different enclosures were divided with moats not visible to the public, and the successive enclosures were higher than the one in front. The exhibits were landscaped with plants and artificial rocks. The artist for the artificial rocks was Urs Eggenschwyler. This gave the public the impression they were seeing the animals together in one natural habitat. After initial skepticism, many zoological gardens throughout the world adopted Hagenbeck's ideas and replaced traditional enclosures. Edinburgh Zoo, for example, was one of these institutions inspired by Hagenbeck’s new design. Then there are the extraordinary artificial mountains of concrete, like the Mappin Terraces in London Zoo, designed in 1913-14 by Peter Chalmers Mitchell and John James Joass.  Even if this kind of exhibiting animals to the public was revolutionary in the history and evolution of zoo design, the actual space provided to the animals remained relatively small and was, in fact, not different from that of the traditional enclosures. The new panoramas benefited the aesthetic sense of visitors and can be seen as mainly anthropocentric constructions.
At the beginning of the twentieth century, new approaches were also made to integrate modern style into zoo architecture. The Jugendstil buildings (1909-1912) at Budapest Zoo in Hungary were ornamented with carved animals. The Jugendstil pavilions of the Elephant House date of 1911 and were designed by Károly Kós. 
During the 1930s, some attempts were made to introduce abstract design into the modern zoo architecture, like those famous abstract geometrical structures by Lubetkin in Regent's Park, Whipsnade and Dudley.  London Zoo's penguin exhibit designed in 1934 by Berthold Lubetkin and the Tecton Group was a icon of the Modern Movement with its sweeping, interlocking concrete ramps above the pool. 
From the 1950s on, first attempts were made to integrate the behavioural needs of the animals into zoo design. This approach based on the ideas of Swiss zoologist Heini Hediger who published his book Wild Animals in Captivity in 1942, translated into English in 1950. In this work he gave cogent arguments for a biological and particularly behavioural approach to zoo design and animal care.But the attempts to integrate the knowledge about animal behaviour into zoo design were often ineffectual and not consequently implemented. More important than behaviour and welfare of the animals remained hygienic aspects and, above all, architectural innovation such as New Brutalism. The Elephant and Rhino Pavilion at London Zoo, designed by Hugh Casson and built 1962-1965, is such an example. Most enclosures constructed from the 1950s to the 1970s were sterile and small cages made of concrete or ceramic tiles. Meeting hygiene standards became important which resulted in enclosures resembling bathrooms. Few zoos adopted these techniques of "sanitary modernist" design more thoroughly than the one in America, Philadelphia Zoo which opened exhibits Carnivora House in 1951, Monkey House in 1958 and Rare Animal House in 1965. 
Due to limited space and a lack of financial means it still remains difficult to construct adequate enclosures, particularly for large animals and their requirement for a sizable territory. According to animal rights groups, zoos lacking the financial means or the interest in constructing more elaborate enclosures still keep their animals in inadequate conditions. These conditions can cause stereotypic behavior.Elephants in zoos can also often suffer from arthritis and foot disease. Only some zoological gardens are able to raise enough funds and have sufficient space to build more adequate enclosures for these animals. Such an example is urban Cologne Zoo, Germany, which opened in 2004 an indoor and outdoor elephant enclosure of about five acres. Norman Foster's new addition to Copenhagen Zoo opened in June 2008 as an extension of Frederiksberg Gardens, the royal park in Copenhagen. The new Elephant House covers approximately 10% of the entire zoo site.  At the end of 2001, the London Zoo's elephants were moved from Regent's Park to Whipsnade Wild Animal Park in Bedfordshire, ending a 170-year tradition of keeping elephants at the city site.  In 2006, three American zoos (Lion Country Safari, Philadelphia Zoo, Gladys Porter Zoo) announced the closure of their elephant exhibits due to a lack of space. Two other zoos, Bronx Zoo and Santa Barbara Zoo, announced the phase-out of their elephant exhibits.
 Landscape immersion
During the 1980s many zoological gardens, first in the United States, changed their policy of designing animal enclosures. The so called "landscape immersion", a term coined by Seattle architect Grant Jones, transformed visibly the outlook and appearance of many zoos throughout the United States. The idea and concept of landscape immersion combines a naturalistic and realistic imitation of natural habitats with the environmental needs of the animals. It was developed by several landscape architects during the wholesale renovation of Woodland Park Zoo in Seattle in the late 1970s encouraged by zoo director David Hancocks. The first landscape immersion exhibit, an enclosure for gorillas, designed by Johnpaul Jones, opened in 1978 at Woodland Park Zoo. For the first time, zoo gorillas had trees to climb, places to hide, a complex landscape to explore, and live vegetation to interact with. According to the original idea and philosophy of landscape immersion the visitors are given the sense they were actually in the animals' habitat. Buildings and barriers are hidden and vegetation plays a dominant role. One of the best examples in Germany is the Erlebnis-Zoo Hannover (Hanover Zoo), an EXPO 2000 project, now featuring six different zoo worlds.
Specific forms of exhibit that can also be referred to landscape immersion are walk-through enclosures and walk-in aviaries. A few European zoos had already realized such exhibits before the term landscape immersion was coined. These ideas were integrated into the concept of landscape immersion and consequently advanced. In contemporary zoos, there are a lot of walk-through exhibits where visitors enter enclosures of non-aggressive species, particularly for birds and small primates. Visitors are asked to keep to paths and avoid showing or eating foods that the animals might snatch. The animals are not tame. One example is Apenheul Zoo, Netherlands, where visitors can get into direct contact with squirrel monkeys and lemuridae on moated islands.
Associated with these changes of zoo design are large tropical indoor exhibits. Bronx Zoo’s 37,000-square-foot (3,400 m2) Asian rainforest "Jungle World", opened in 1985, is a pioneer exhibit of its kind. Leipzig Zoo, Germany, is currently building a similar, but more giant project, the so called "Gondwanaland". The transformation of zoos according to the concept of landscape immersion is slow and still in progress since the changes require extraordinarily financial and technical expenditures.
 Special enclosures
Zoos may have special buildings for nocturnal animals, with dim white or red lighting used during the day, so the animals will be active when visitors are there, and brighter lights at night to help them sleep. Special climate conditions are created for animals living in radical environments, such as penguins which are kept in refrigerated rooms. Special enclosures for reptiles, amphibians, insects, fish, and other aquatic life forms have also been developed.
 Management and animal care
Related and similar institutions in aims, staff and history are public aquaria. At the time when the first zoological gardens were established during the nineteenth century also public aquaria came into existence. Today, both zoos and public aquaria are integrated in the same national and international umbrella organizations. These zoo associations proclaim to force their members to achieve certain standards in animal management, veterinary care, aims, and stewardship.
The International Species Information System (ISIS), a computer-based inventory system, was established in 1973 to facilitate collection and population management for wild animals maintained in captivity. 
Most zoological gardens incorporated within international umbrella organizations are led by professionals such as zoologists or veterinarians.
Curators plan for the development, maintenance, and growth of the animal collection and animal care staff. They are responsible for the acquisition of animals and play a role in the administration of captive breeding programs. They also participate in scientific conferences, write scientific papers, or assist in exhibit design.
Veterinarians provide medical care for ill or injured animals including surgery, vaccinations and physical exams. They also develop and implement preventive health care, or help determine healthful animal diets.
Responsible for the actual care of the animals within these institutions are zookeepers. The training of a zookeeper is very broad and covers many areas of modern animal husbandry, basic veterinary knowledge, behavioural biology knowledge.  Some keepers can become highly specialized such as those who concentrate on a specific group of animals like birds, great apes, elephants or reptiles. Daily basic duties of zoo keepers include cleaning and maintenance of animal enclosures and feeding of the animals. Some keepers prepare animal diets, report and record animal's health and behaviour, or assist veterinarians. The educational requirements for an entry level zoo keeper vary but are often a college degree in zoology, biology or an animal-related field. Some colleges offer programs oriented towards a career in zoos. Job advancement is also possible but more limited than in some other careers requiring a college degree. Some zoos, particularly roadside zoos, are private-owned amateur facilities with a lack of well trained personnel.
 Animal care
The physical health as well as the social and behavioral well-being of zoo animals depends on enclosure design, nutrition, husbandry, management practices, group social structure, behavioral enrichment, preventive medicine, and medical and surgical care. 
Most contemporary zoos led by professionals are aware of environmental enrichment, also called behavioral enrichment, as a part of the daily care of animals. Environmental enrichment refers to the practice of providing animals with environmental stimuli. The goal of environmental enrichment is to improve an animal's quality of life by increasing physical activity, stimulating natural behaviors, and preventing or reducing stereotypical behaviors. 
But sometimes even those zoos proclaiming high standards can fail to meet them in some way. Accidental deaths during the six months of animal stocking preceding the opening of Disney's Animal Kingdom were investigated by the United States Department of Agriculture (USDA) in 1998.  After a series of publicized animal deaths at the Smithsonian Institution’s National Zoological Park (National Zoo) in early 2003, the National Academies released an interim report in 2004 and an final report in 2005.  Another example is the captive breeding management of great apes where these animals and their infants are traded and shuttled from place to place.
Because they wanted to stress conservation issues, many large zoos stopped the practice of having animals perform tricks for visitors. The Detroit Zoo, for example, stopped its elephant show in 1969, and its chimpanzee show in 1983, acknowledging that the trainers had probably abused the animals to get them to perform.
Some zoo practices in countries without animal protection laws would be illegal in many countries. Some examples include:
- The Badaltearing Safari Park (China) encourages zoo visitors to throw live goats into the lions' enclosure and watch them being eaten, or purchase live chickens tied to bamboo rods to dangle into lion pens. Visitors can drive through the lion's compound on buses with specially designed chutes leading into the enclosure into which they can also push the live chickens.
- Xiongsen Bear and Tiger Mountain Village (near Guilin in south-east China) feed live cows to tigers to amuse visitors.
- Qingdao Zoo, (near Beijing, China) allows visitors to engage in "tortoise baiting", in which they are encouraged to throw coins at the turtle's heads. The turtles have elastic bands around their necks, so that they can't retract.
 Acquisition and surplus of animals
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Controversy surrounded the importation of seven African elephants (an officially endangered species) from the wilds of Swaziland to the San Diego Wild Animal Park in 2003, despite offers to move the elephants to reserves elsewhere in Africa. Prior to the import, three resident elephants were shipped to Chicago's Lincoln Park Zoo, where all three elephants died within two years.  There have been births from the Swaziland elephants since coming to the Wild Animal Park. In 2008, the Wild Animal Park houses eleven African elephants in a 3 acres (12,000 m2) enclosure. 
The downside to breeding the animals in captivity is that thousands of them are placed on "surplus lists", and sometimes sold to circuses, animal merchants, auctions, pet owners, and game farms. The San Jose Mercury News conducted a two-year study that suggested of the 19,361 mammals who left accredited zoos in the United States between 1992 and 1998, 7,420 (38 percent) went to dealers, auctions, hunting ranches, unaccredited zoos and individuals, and game farms. Some zoos have advertised surplus animals in the Animal Finders' Guide, a newsletter in which the owners of hunting ranches post notices of sales and auctions.
A German Greens Party politician alleged in March 2008 that hundreds of the Berlin Zoo's 23,000 animals are missing, amid allegations that they have been slaughtered, and that some tigers and leopards were sent to China to make drugs for traditional Chinese medicine. The Director of the zoo replied by saying he believes his detractors are spreading "untruths, half-truths and lies".
Many countries have legislation to regulate zoos that requires these institutions to be licensed and inspected. Zoo regulation is usually supported by written standards relating to species, exhibits and management. 
In the United States, any public animal exhibit must be licensed and inspected by the United States Department of Agriculture, United States Environmental Protection Agency, Drug Enforcement Agency, Occupational Safety and Health Administration, and others. Depending on the animals they exhibit, the activities of zoos are regulated by laws including the Endangered Species Act, the Animal Welfare Act, the Migratory Bird Treaty Act of 1918 and others. Additionally, zoos in North America may choose to pursue accreditation by the Association of Zoos and Aquariums (AZA). To achieve accreditation, a zoo must pass an application and inspection process and meet or exceed the AZA's standards for animal health and welfare, fundraising, zoo staffing, and involvement in global conservation efforts. Inspection is performed by three experts (typically one veterinarian, one expert in animal care, and one expert in zoo management and operations) and then reviewed by a panel of twelve experts before accreditation is awarded. This accreditation process is repeated once every five years. The AZA estimates that there are approximately 2,400 animal exhibits operating under USDA license as of February 2007; fewer than 10% are accredited.
In April 1999, the European Union introduced a directive to strengthen the conservation role of zoos, making it a statutory requirement that they participate in conservation and education, and requiring all member states to set up systems for their licensing and inspection. Zoos are regulated in the United Kingdom by the Zoo Licensing Act of 1981, which came into force in 1984. The act requires that all zoos be inspected and licensed, and that animals kept in enclosures are provided with a suitable environment in which they can express most normal behavior.
Main entrance of San Diego Zoo.
A painting of the London Zoo in 1835.
Artists at the Ménagerie du Jardin des Plantes (Painting from 1902).
Giant Panda enclosure at Chiang Mai Zoo.
Aquarium with a dolphin at the Barcelona Zoo.
Sea lions at the Melbourne Zoo.
A jaguar statue in Rio de Janeiro's Zoological Garden.