Zoos and aquariums exhibit many rare species, but sustain few for long periods. Demanding genetic, demographic, and behavioral requirements are a part of the sustainability challenge, and historical zoo goals and limiting animal management objectives are another, but they have been overtaken by worldwide wildlife population contraction and endangerment. New policies are essential for zoo continuance and, if vanishing species are to be helped by zoo propagation, they must be given priority. However, zoos have little animal carrying capacity and propagation must be much more sharply focused. In addition, it is becoming urgent that zoos help to support parks and reserves and, where possible, manage some especially endangered species mutually with parks. Zoo Biol 29:1–8, 2010. © 2010 Wiley-Liss, Inc.