Soundscape composition, sound design for film and game sound commonly use audio databases or libraries of sound files. Different audio databases use different strategies to help users search, retrieve and contribute sound data. This chapter explores the characteristics of online audio databases beginning with a review of the core literature on cataloging sound files by taxonomy, ontology representation and collaborative tagging. A general outline of database environments is examined, focusing on the user-contributed model, expertly managed databases and sound maps. We frame these developments in the context of soundscape composition. Finally, we provide a guide to the characteristics of the databases discussed in this article for those wanting to utilize these assets in research and production.