Papers relating to Siegfried Loraine Sassoon accumulated by his biographer Max Egremont. The papers are arranged in two series: correspondence and research files.

The correspondence includes Sassoon's incoming and outgoing letters, and letters received by various family members. A number of photographs of Sassoon are included with the letters. Sassoon's correspondence includes a large series of letters from his mother, Georgiana Theresa Sassoon (née Thornycroft, known as Theresa) spanning several decades, together with letters to his wife Hester (née Gatty), and to the bookseller P.H. Muir, and letters received from friends such as Sir Edmund Gosse, Edith Olivier and Laurence Whistler. There are also sets of letters received by Sassoon's relatives: Theresa Sassoon, Hester Sassoon, and his mother in law, Katherine Gatty. Significantly, the letters to Theresa Sassoon include three from Siegfried's brother Hamo dating from the First World War, together with letters on Hamo's death in action in 1915, including two written by Siegfried Sassoon.

The research files include a large set of press cuttings of Sassoon's writings and reviews, papers concerning Sassoon's friendship with Dame Felicitas Corrigan, copies of tributes to Sassoon, transcripts of reminiscences by his son George Sassoon, and Max Egremont's own research notes.