thumb|upright|Siberian Tiger at the Aalborg Zoo, Denmark. A zoo, an abbreviation of zoological garden, 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.

Collections of wild animals were displayed in the 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.

The aims of zoo professionals have traditionally ranged from public education to conservation of biodiversity, as well as recreation.Tribe, Andrew, "Zoo Tourism", in Wildlife Tourism: Impacts, management and planning, Higginbottom, Karen (ed.), Common Ground Publishing, Altona, Victoria, 2004, pp.35-56. ISBN 1-86335-545-6 Many zoos define their aims as 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. Zoos are frequently criticized by animal rights groups for varied reasons, including the quality of life of the animals they exhibit, and the perceived necessity or purpose of exhibiting captive animals at all.

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.

Etymology

The terms zoo and zoological garden, that refer to zoology (from Greek: ζῷον, zoon, "animal"; and λόγος, logos, "knowledge"), did not come into use until the modern zoo concept developed during the nineteenth century. London Zoo, launched in 1828, is the first place where wild animals are exhibited in captivity, to be called a "zoological garden" and, after 1829, when land on the opposite side of the road fronting the main gate was acquired, in the plural form "zoological gardens".Reichenbach, Herman, "Lost Menageries: Why and How Zoos Disappear (Part 1)", International Zoo News Vol.49/3 (No.316), April-May 2002, pp.151-163. 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 print 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".