Politics: correspondence, drafts of articles, and transcripts of lectures concerning his involvement in the Irish revolution including his membership of the Irish Volunteers, his unsuccessful gun-running expedition to the US, his dismissal from the National Museum following the Easter Rebellion, his internment in Frongoch and his subsequent withdrawal from political activity, 1912–76.

National Museum of Ireland: correspondence relating to his dismissal from the National Museum, his reinstatement, his secretaryship of the Victimised Civil Servants Association, disputes over promotions and grading within the Museum, disputes with the Royal Irish Academy, applications for posts outside the National Museum and his retirement, 1916–56. Correspondence and newspaper cuttings relating to his period of employment in the Irish Antiquities division of the National Museum, 1926–34. Correspondence, diaries and newspaper cuttings relating to his period of employment in the Art and Industrial Division of the National Museum, 1934–64. Correspondence relating to the establishment of regional museums, particularly a Dublin Municipal Museum, 1928–64. Drafts of articles, transcripts of lectures and broadcasts relating to his work in the National Museum, 1934–69.

Archaeology: articles, pamphlets, texts of lectures, and correspondence relating to national developments in Irish archaeology, 1920–33. Correspondence, articles and photographs relating to the Harvard Archaeological Expedition to Ireland, 1932–34. Drafts of articles and transcripts of lectures relating to the study of prehistoric Ireland, 1928–60. Correspondence, newspaper cuttings, sketches, maps, articles and photographs relating to archaeological finds in Leinster, Munster, Connacht and Ulster, 1898–76. Correspondence, pamphlets, articles, transcripts of lectures, and photographs relating to the study and discovery of common archaeological features and artefacts in Ireland, 1870–1957. Correspondence, photographs and articles relating to the study of specialist areas of Irish archaeology, such as peatland archaeology, ecclesiastical archaeology and human palaeontology, 1899–1950. Drafts of articles, newspaper cuttings, photographs, sketches and correspondence relating to aspects of international archaeology, 1905–78. Correspondence, articles, transcripts of lectures, notes, newspaper cuttings, sketches, drawings, maps, and photographs relating generally to his archaeological research and excavations, 1894–1971.

Poetry: correspondence relating to the publication of six volumes of poetry, 1918–79. Newspaper cuttings and other printed matter relating to publication of his poetry in serial publications, 1912–63. Newspaper cuttings, correspondence, articles and notes relating to the translation of his own poetry into English and other poets’ works from their native languages into Irish, 1920–77. Typescript and holograph drafts of poetry, 1918–65. Correspondence, newspaper cuttings, drafts of articles, and lecture transcripts relating to his poetry and Irish poetry generally, 1928–73.

Lexicography: correspondence, notes, and drafts relating to the compilation, submission, rejection, resubmission, and attempted publication of his MA thesis, Foclóir na hÁrdshaoirse agus a Cóimhchéard, 1888–52. Correspondence, drafts, notes, articles and lists relating to the compilation and publication of Foclóir Gaedhilge-Béarla comp. P.S. Dinneen, 1927, 1907–76. Correspondence relating to the disputed supplement to the Dineen dictionary prepared by Gógan for the Irish Texts Society, 1935–74. Correspondence relating to the life and death of P. S. Dinneen, 1929–58. Correspondence and articles relating to general lexicographical matters, 1936–76.

Irish language revival: correspondence, minutes, and articles relating to Conradh na Gaeilge, An Cumann Gaedhealach, An Comhar Drámaíochta and other Irish language organisations, 1916–70. Correspondence, articles, and newspaper cuttings relating to the revival and ‘re-gaelicisation’ of Ireland, English-Irish translations, Roman and Gaelic typography, and Irish placenames, 1920–79.

Celtic Studies: correspondence between Gógan and Julius Pokorny, 1935–49. Correspondence, reports, and newspaper cuttings relating to the International Celtic Congress, 1934–56. Pamphlets, articles, and correspondence relating to the study of Q-Celtic, 1905–76. Articles, transcripts of lectures, printed matter, notebooks and correspondence relating to the subject of Celtic mythology, 1918–78.

Christian studies: correspondence, minutes, reports, articles, and newspaper cuttings concerning the administration of the Academy of Christian Art, 1928–57. Correspondence, articles and photographs relating to the publication of Gógan’s The Ardagh Chalice, 1932. Drafts of articles, printed matter, photographs and correspondence relating to diverse aspects of Christian art, 1927–72. Draft articles, notes, correspondence, newspaper cuttings and other printed matter relating to the life of St Patrick, 1918–78.

Folklore: correspondence, minutes and articles relating to membership of An Cumann le Béaloideas Éireann and An Cumann Seanchais, 1927–40. Articles, newspaper cuttings, notes and correspondence relating to the study of Irish folklore, 1930–69.