The use of contextual information about the creators and users of archival and manuscript resources has always been a critical method for discovering and providing access to them. Traditionally, this information has been unstructured and ephemeral, being part of the knowledge that experienced staff bring to reference queries. The development of Encoded Archival Context provides a methodology and structure for recording this information about the characteristics of creators and the circumstances of creation more explicitly and in ways that it can be used to support discovery of archival and manuscript sources. (Contains 13 notes.)