The Online Archive of California is a collaborative project to create a searchable online union database of finding aids to archival collections. This database includes the finding aids to repositories from 40 institutions statewide, including all nine UC campuses and is continuing to expand. A small but increasing number of the finding aids contain links to online digital versions of the source material. Finding aids are inventories, registers, indexes or guides to collections held by archives and manuscript repositories, libraries, and museums. Finding aids provide detailed descriptions of collections, their intellectual organization and, at varying levels of analysis, of individual items in the collections. Access to the finding aid is essential for understanding the true content of a collection and for determining whether it is likely to satisfy a scholar's research needs. For a detailed description on how to use primary source materials and their associated finding aids see: Library Research Using Primary Sources