Auldbar was bought in 1753 by William Chalmers, a Gibraltar merchant whose family had owned land in Aberdeenshire, at Federate and Hazlehead. His father and brother were physicians in Aberdeen, and the papers as arranged below begin with medical records of these men. An important section concerns the trade and administration of Gibraltar in the second quarter of the 18th century, and there is also much mercantile correspondence of the 18th and early 19th centuries. As with the rest of this collection the estate papers and accounts are fragmentary and lacunose, and they came to the Library in poor condition. Large periods, particularly in the later 19th century are not represented, and there is comparatively little on the Chalmers family estates before the purchase of Auldbar. Building operations and improvements at Auldbar Castle are covered in a certain amount of detail in correspondence, specifications and accounts. The legal correspondence and papers of the family have survived in quantity. Several fields in which various members of the family were interested or even prominent have been accorded sections by themselves - medical practice and mercantile activities have already been mentioned - and these include political affairs (Patrick Chalmers (died 1854) was M.P. for Montrose Burghs 1855-1842) and patronage disputes; ecclesiastical affairs, including patronage matters; antiquarian and genealogical research, on which Patrick Chalmers M.P. was a leading Scottish authority (there are included here groups of letters from some of the leading antiquaries of the day); and there is a section of papers concening railway companies in which Patrick Chalmers was involved. Educational, cultural and literary matters are the subject of a separate section.
The correspondence of a fair number of members of the Chalmers family, together with their connections, has been preserved, though here again the coverage is patchy. Notable sections are the personal correspondence of Patrick Chalmers (died 1824) with his son, a London merchant, and his daughter-in-law, and with his female cousins. There are runs of correspondence with the Elphinstone, Guthrie, Spankie and Inglis families, all connected by marriage with the house of Auldbar. Letters concern military service in India, Egypt and the Sudan; colonial life in South Africa, Australia and New Zealand; and business activities in London or the Empire. The affairs of the Vernon family of Hanbury Hall, Worcestershire, into which the antiquary Patrick Chalmers's wife had first married, are treated in a separate section. A number of miscellaneous sections and single items bring the papers to a close.
The Chalmers Papers were surveyed by the National Register of Archives (Scotland) in 1963. On the subsequent sale of Auldbar Castle the muniments were dispersed and many items noted in 1963 have not since been located.