Zoological parks make up a highly heterogeneous community. Ranging from small collections at shopping malls to highly developed bioparks, their contribution to conservation is expected to vary enormously. Although several studies have focused on assessing such contribution, the parameters used frequently do not apply when considering more modest zoos. The goals of this study are to determine, within the wide range of zoos, which type tend to fulfill the conservation mission of modern zoos and to identify the variables associated to their conservation performance. We used the requirements demanded by the European Community Zoos Directive 1999/22/EC, relating to the keeping of wild animals in zoological parks, to assess conservation performance in 72% of officially registered Spanish zoos. Sampled zoos were classified into groups according to their common characteristics, and then the variables related to how they met each of the Directive's requirements in the groups were assessed. We found that private zoological parks with large zoological collections, located within metropolitan areas, and members of a zoo association tended to fulfill the requirements. Being a member of a zoo association was the variable that better explained fulfillment of the requirements among the evaluated zoos. Data revealed that zoos not meeting any requirement were few, although those meeting all of them were not frequent. The requirement related to adequate record keeping showed the lowest level of fulfillment. We discuss the implications of our results and propose measures of change in order to promote the contribution of zoos to biodiversity conservation. Zoo Biol 31:55;–70, 2012. © 2011 Wiley Periodicals, Inc.