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.