This book provides a scholarly edition of the letters of A. S. Rowntree, prominent businessman and Quaker, to his wife, M. K. Rowntree. The letters cover the period 1910-1918, during which he was Liberal MP for York. The edition provides a unique window into the under-explored world of backbench Liberal MPs, especially those committed to the New Liberalism. It shows that the activities and opinions of MPs in this period cannot be understood without reference to the wider context of their lives, especially their religion, business interests and charitable work. The letters also provide significant new information on developments in Quaker thinking on social and political issues, the problems faced by pacifist MPs in World War One and how gender identities were constructed within political marriages in Edwardian Britain.