The collection contains around 4,300 letters, of which the majority are between Martin Conway and his relatives, principally his parents William and Elizabeth Conway; his first wife Katrina, and her mother and stepfather, Abigail and Manton Marble; and his daughter Agnes and her husband George Horsfield. Of correspondents outside the family, only letters to and from Henry Bradshaw and Karl Pearson (the latter nearly all typed copies) survive in any great numbers. The collection also includes an almost complete series of diaries covering the adult life of Martin Conway, as well as the diaries of William Conway and Agnes. There are also miscellaneous papers, which have been only roughly sorted, and relate mainly to Martin Conway.