A knowledge-base management system (KBMS) with the following goals is proposed: (1) to allow a knowledge engineer to update a knowledge base and have these updates persist on secondary storage, (2) to allow multiple knowledge engineers to have shared access to a knowledge base and modify the knowledge base concurrently, and (3) to maintain consistency of the shared knowledge base as it evolves. At the heart of the KBMS is the version store, which is a persistent storage structure that maintains multiple versions of a knowledge base. Retrieve and update operations are defined on the version store to efficiently access and modify any version. Objects in the version store are clustered to support efficient access of an entire version or some subparts of it. To store the effects of an update requires space proportional to the size of the update and which is independent of the size of the knowledge base. The additional cost of maintaining multiple versions is within a small constant factor of maintaining a single version.>