This study explores the concept and functions of collection from the perspective of the user. In-depth interviews with ten professors from a social science discipline and a natural science department provided descriptions of their information seeking involving material sources and their perceptions of the library collection. Participants used the following parameters in perceiving the library collection: instant availability, selectivity, physical collocation, catalog representation, user privilege, material stability, and further parameters for subcollections, including subject and format. Additional components that were important in the users' information environment were personal collections, the Internet, and other institutions' collections. Analysis revealed that collections provided valuable functions, such as collocating sources for convenience and saving time and money, selectivity, narrowing the search scope to increase precision and ease of use, presenting choices, and assisting in clarification of information need. The user's perspective demonstrates the need for user-centered and flexible, rather than library-centered and fixed, collection structures.