The collection contains the surviving foreign mission records to 1929 (with a few documents of the early 1930s) of the churches which in that year reunited to form the Church of Scotland, namely the (Established) Church of Scotland and the United Free Church of Scotland, the latter itself the product of the union in 1900 between the Free Church of Scotland and the United Presbyterian Church.

The bulk of the material consists of the letter-books of the conveners, secretaries, and clerks of the various Foreign Mission Committees, containing their letters both to missionaries and to supporters and others in Britain. Incoming correspondence, mainly from missionaries, is the next largest group. Finally there are a few minute-books, account-books, diaries, volumes of newspaper cuttings, and other miscellanea. The period covered is 1822-1929, but material is sparse until the 1870s. The letter-books are generally in continuous series, with only a few gaps, but the incoming letters are preserved only for brief periods, mainly 1880 to 1905 and 1918 to 1925.