Mac an Bheatha's private and business correspondence comprises items mostly concerning his press work and other publications, some items from friends, and from the reading public. There are few drafts for outgoing letters. The main themes are the Irish language and its promotion in Irish society, and Irish history. Among notable correspondents there are Cardinal Ó Fiaich, Róisín Ní Mheara, Muiris Ó Droighneáin, Gabriel Rosenstock, Ciarán Ó Coigligh, Erna Bennett.
Mostly containing items of correspondence sent to George Gilmore, some reflecting Gilmore's political views, and his later activities as public speaker and contributor to the press.
Mary O'Malley's personal correspondence with family and friends, in chronological files.
Correspondence directly related to Mary O'Malley's political career.
Pearse O'Malley's personal and professional correspondence, in chronological files.
Correspondence with other members of Clan O'Malley, in chronological files.