Audio files for lectures taped before January 2006 are not available on this site. Those lectures can be accessed through the Parks Library University Archives.
A list of available, unrestricted recordings for events between 1970 and 2006 is available here: Unrestricted recordings by date
This list includes speakers cosponsored by the Committee on Lectures, World Affairs Series (formerly the Institute on World Affairs) and National Affairs Series (formerly the Institute on National Affairs). It is not a comprehensive list of events sponsored by these groups.