Zoo Tycoon is a zoo simulation video game putting the player in control of their own fictional zoo business. The gameplay formula introduced in the original Zoo Tycoon in 2001 received updates throughout the series, but its theme and main motifs remain unchanged: Players must build, expand, and/or upgrade a zoo by purchasing animals, creating suitable animal habitats, and allocate staff and resources for animal maintenance and care. As the ultimate goal of the game is revenue, players must also provide for visitors by building food/drink stands, sanitary facilities, picnic areas, and an aesthetically pleasing environment. Higher revenue is generated by keeping both animals and visitors happy. If the animals are released from their enclosure, they can kill the visitors.