This series consists of the official correspondence of the organization. This is grouped by presidential term of office, and includes outgoing and received correspondence by the president, as well as other officials of the ITA. Terms of office ran for two years from mid-year to mid-year with the incoming president taking office at the end of the International Trombone Workshop, usually held in June or July each year.

There is significant overlap between and among the official correspondence and the files of the working committees of the Board of Directors, as well the files of Events, Photographs, Membership, Subject Files and other series. The letters were mostly left where they were found.