This book constitutes the thoroughly refereed post-proceedings of the 9th International Workshop on Persistent Object Systems, POS-9, held in Lillehammer, Norway, in September 2001.The 19 revised full papers presented together with seven session overviews and an epilogue were selected during two rounds of reviewing and revision for inclusion in the proceedings. Among the topics addressed are persistence-enabled optimization, Java applications, JVM, systems architecture, persistent GIS, data sharing middleware, polylingual persistence, transactions, distributed object systems, object stores, garbage collectors, WWW and persistence, persistent computation implementation, orthogonally persistent Java, and personal information devices.