17 letters, mostly in English: 9 November 1963; 10 March 1964; c.March 1964; 7 January 1965 (regarding manuscript section on Ó Direáin and Ó Ríordáin); 16 March 1965; 29 May 1967; Letter to Gordon MacLennan; Letter PÓC to Frank O'Brien 14 July 1967; 9 August 1967; 10 October 1967; 18 December 1967; 26 January [1968]; Letter from An Clóchomhar 17 March 1968; Letter from Coiste na Leabhar 28 February 1968; 23 May 1968; 7 October [1968]. The letters refer to O'Brien's Filíocht Ghaeilge na Linne Seo. Translation was carried out by Aodh Mac Dhúbháin. See also the letter from Tomás Ó Concheanainn.