This dissertation seeks to address two key themes, drawing on archives in Britain, the United States, and Greece. Firstly, it examines the impact of British Intelligence on the Greek war effort, resistance to Axis occupation, and the period after liberation, by examining the changing role of intelligence in each period. During the early part of the war, the Intelligence Services, and in particular the newly founded Special Operations Executive, sought to achieve their aim of stoking resistance in Greece to help the British war effort through a number of operations. The failure of these operations, however, would have a lasting impact on their future work in Greece. After the stunning success of SOE Operation ‘Harling’, British officials in Cairo and London increasingly fostered guerrilla warfare, making their mission in Greece extremely complex. This was particularly true of SOE, which now entered the hazardous world of guerrilla politics even as it was now serving an equally important political and diplomatic role. While relations between the British and EAM (the communist-led National Liberation Front) had initially been cordial, relations soured as the war progressed and post-war ambitions became more pressing. Eventually, the understanding between the two sides broke down completely and, only a few months after the liberation of Greece, the British government was in open conflict with the guerrillas of EAM. This leads on to the second key theme of the dissertation: the ramifications of the involvement of British Intelligence on the Greek Civil War, and in particular the effect of the dual policy followed by the British in Greece, trying to achieve what proved to be mutually exclusive military and political aims. It will also seek to elucidate whether British involvement in Greece helped to exacerbate the conditions in Greece which led to Civil War, an ongoing topic of scholarly and public controversy.