The archive of the Royal Celtic Society, founded in 1820 as the Celtic Society, and bearing its 'Royal' designation since 1873. Among the founder members were Captain William Mackenzie of Gruinard, Sir David Stewart of Garth and Sir Walter Scott, the Society's first vice president.

The archive contains minute books, financial records, membership lists, correspondence, files on the Society's history and constitution, photographs, newspaper cuttings and miscellaneous matter.