User Expansions are expansion packs for the base Zoo Tycoon 2 game made by fans and designers that have not been directly authorized by Blue Fang Games or Microsoft. They imitate official expansion packs by generally adding roughly 15-25 animals and a variety of bonus content, including a filter and an icon on the main menu.
The first user expansion team was Artifex, which formed in 2006 and created the Arabian Nights and Island Excursions user expansions, and disbanded during production on the latter. The second was Kryptids, which only lasted a few weeks. Worldwide Designers United, another early team, lasted for three years, completing a BETA version of Worldwide Wonders.
Only one user expansion was every completed for the original Zoo Tycoon, known as Wild Wings, created by RSN in 2003.