The San Diego Zoo is a zoo in Balboa Park, San Diego, California, housing 4000 animals of more than 650 species and subspecies on 100 acres (40 ha) of Balboa Park leased from the City of San Diego. Its parent organization, San Diego Zoo Wildlife Alliance, is a private nonprofit conservation organization, and has one of the largest zoological membership associations in the world, with more than 250,000 member households and 130,000 child memberships, representing more than a half million people.