At the outbreak of the Second World War, international humanitarian law was made up of the various Hague Conventions of 1907 and the two 1929 Geneva Conventions, none of which dealt in a satisfactory manner with the risks faced by the civilian population. Experience during the war made a major revision of international humanitarian law a priority after 1945. This articles traces the history of that endeavour up to the adoption by a diplomatic conference, on 12 August 1949, of the four Geneva Conventions for the protection of war victims. Particular emphasis is laid on the link between the ICRC's wartime experience with the inadequate law of the day and the negotiations for new legal provisions. The second part of the article identifies the major advances represented by the 1949 Geneva Conventions, one of the more important being the fact that the law's scope was extended to non-international armed conflicts. Though making no claim to perfection, the new Geneva Conventions nevertheless laid a sound basis on which adequate solutions may be found when military considerations and humanitarian exigencies clash.