Union catalogs have yet to reach their full potential on the national level or in California. The National Union Catalog and the Union List of Serials in the Libraries of the United States and Canada, although monumental efforts, are far from comprehensive. A survey found that California exhibits most of the problems involved in union catalog efforts anywhere. The state library has a union catalog of 81 participating libraries and is compiling a union list of the periodicals of over 1000 libraries. The University of California compiles union catalogs and lists for its campuses. Union catalogs are also produced in many of the state's 21 public library systems. Further cooperation is planned between different types of libraries. To make optimum use of these diverse efforts, coordination at the state level is needed. (PF)