One of the benefits of becoming a member of your local AZA-accredited zoo or aquarium is free or discounted admission to AZA-accredited zoos and aquariums that participate in the AZA Reciprocal Admissions Program. Here's the recently updated List of participating zoos and aquariums (PDF) for 2018.
Be sure to read the Reciprocal Admissions Program Rules before visiting the zoos and aquarium on this list. Please note that participating institutions located in close geographic proximity to each other are not required to offer free or discounted admission to each other's members in order to participate in the Reciprocal Admissions Programs, although they may offer an alternative discount. It is always a good idea to call ahead.
Some AZA-accredited zoos and aquariums that do not participate in the AZA Reciprocal Program may have individual reciprocal agreements with other AZA-accredited zoos and aquariums. Contact your local zoo or aquarium to find out about any special discount arrangements.