How repository libraries contribute effectively to the fabric of collection development and management

Recent statistical compilations provide clear evidence that individual libraries are collecting a declining proportion of the world's expanding publishing output from both commercial and other sources. Collaboration among libraries is essential if they are going to provide the quality of collections and services required by increasingly sophisticated in-formation-hungry readers. Such co-operation involving shared collections falls into two models: one based on decentralised collecting in which individual libraries assume responsibility for selected subjects or formats, and centralised collecting in which a single library assumes responsibility for collections that supplement those of the participating libraries. Examples of both are provided with conclusions about their respective strengths and weaknesses. A centralised collection may also provide repository services to its collaborators, which assists in easing the pressure of crowded, local shelving. What types of collections are best suited to a repository with collection management responsibilities? What other roles can repository libraries play in interlibrary co-operation?