As zoos have evolved, conservation and conservation education have become primary tasks. To achieve the maximum educational impact, zoos are enriching animal habitats so that their occupants display a wide range of activities that are attractive to the visitor, and unattractive activities are eliminated and reduced. Because public perceptions of the attractiveness of animal behaviour may not coincide with welfare realities, there can be a tension between the requirements of desirable exhibits and those of maximally promoting animal welfare. Zoo animals differ from domesticated animals in human care in several respects. These differences are discussed and set in the context of the sometimes competing aims of enhancing welfare and promoting educational exhibits. An outline history of zoo enrichment programmes suggests that the subject is in need of systematization. The range of data available for improving zoo exhibit designs, and the lives of zoo animals, is reviewed. It is concluded that fundamental data on the environmental needs of many of the wild animals maintained in zoos are deficient in many important areas. Consequently, there is an urgent need to increase such research. Zoo habitats could be excellent places for such fundamental studies, which would feed back into field studies. At the same time, habitat enrichment in zoos cannot await such research and must proceed pragmatically using the range of insights described in this paper. In particular, functional substitution is advocated as a means of enrichment wherever this can be made acceptable to the broad public; its educational value in combatting naive anthropomorphism is stressed. Naturalism in enrichment is criticized as reinforcing anthropomorhisms, but is desirable for promoting global habitat conservation.
