The thesis looks at a previously unstudied topic: non-partisan humanitarian relief by international agencies during the Spanish Civil War (1936-39). It defines these agencies as those offering aid independently of governments and to both sides in the conflict. Thus the thesis covers: the British and American Quakers; the International Committee of the Red Cross (ICRC); the Save the Children Fund, Britain (SCF) and the Save the Children International Union, Switzerland (SCIU); together with Service Civil International, Switzerland (SCI) and. later in the conflict, one ad-hoc co-ordinating agency, the International Commission for the Assistance of Child Refugees in Spain (IC).  This study constitutes the first fully documented history of the humanitarian work of these agencies in the conflict. It covers the conduct of the agencies; their interactions, diversities and similarities; the problems, successes and failures in their work at the start, during and at the end of the Spanish Civil War; and the way they interacted with the political authorities on both sides of the conflict. It offers an analysis of cases and situations not addressed before, while also offering its own reassessment of other controversial topics: for example, Franco’s attitude towards foreign humanitarian aid; the work of the American Quakers and the SCIU in Francoist Spain; and the question of the “safe zone” in the North as an alternative to the evacuation of refugee children.  The contribution of this thesis lies in its coverage of a number of different agencies and their interaction.  It discusses the different approaches of British and American Quakers, shedding light on the respective histories of these two branches of Quakerism, and on the workings of humanitarian relief in the two zones of wartime Spain (Republican and Francoist). It also describes personalities such as Mme Frederique Small of the SCIU and Rodolfo Olgiati of SCI, so important for the relief effort in Spain, whose activities have been virtually omitted by other historical works. As an initiatory study, it also offers an archival “map” of primary material that can assist future researchers