This collection contains correspondence to and from members of Hilaire Belloc's immediate and extended family. It features correspondence between Belloc and his three sons: Louis, Hilary, and Peter; his sister, Marie Belloc Lowndes; and his mother Bessie Raynor Parkes Belloc. Researchers should note that members of the Belloc family tend to anglicize each other's names in their correspondence, thus Hilaire becomes Hilary and Marie becomes Mary in much of this collection.

It also contains correspondence from Marie Belloc Lowndes' son-in-law and daughter, Luiz and Susan Belloc Lowndes Marques. Correspondence between Belloc and his brother-in-law, Frederick Lowndes, his nephew and niece, Charles Lowndes and Lily Belloc Lowndes, and his sister-in-law, Elizabeth Hogan, is also included.