The paper provides an analysis of the foreign volunteers’ intervention in France during the First World War. It discusses the activities of the US humanitarian relief, that from the Franco-Prussian War evolved into permanent structures such as the American Relief Clering House (ARCH) and the American Ambulance Field Service (AAFS) and also analyzes the phenomenon of American volunteers in the French army and in the organization of the Lafayette Escadrille. Particular note is given to the phenomenon of American ambulance volunteers in the Harjes Formation and Norton's Motor Ambulance Corps. It is also described the evolution of the humanitarian activities of the volunteers and the contribution of Anglo-American diplomats organization of relief efforts both in France and in Belgium. In particular, the paper describes the birth and development of the two major associations of US humanitarian relief, the American Field Service (AFS) in France and the Commission for Relief in Belgium (CRB) and the contribution to the latter organization by Herbert Hoover.