From the 1930’s to the 1950’s a significant number of left-wing men and women in the United States, Britain, Europe, Australia and Canada were recruited to the Soviet intellgence services. These people were amateurs, rather than professional intelligence workers and the reason for their success is intriguing and has never been satisfactorily explained. Using recently released Soviet archives, this book seeks to explore the foundations for these successes in the deliberately concealed tradition of underground political activity which was part of the communist movement. This tradition, which became extremely useful to Soviet intelligence, also explains the origins of the tradecraft of espionage. The book seeks to contribute to the study of the causes of the early Cold War, by explaining how this underground tradition lead to espionage. This title shows that while allegations of disloyalty during the Cold War were often part of a witch-hunt, the Left and their liberal allies sometimes unwittingly had a number of skeletons in their closet.