During the Second World War, Switzerland, which remained neutral, was the scene of an intense activity of espionage. While the German border guards monitored the France-Switzerland border, the Allied secret services made Switzerland the hub of their clandestine operations. Gradually, a secret collaboration was organized between the Swiss Intelligence Service and their French, British, Polish, Belgian, and American counterparts. This history presents two perspectives: that of the federal institutions, torn between a centuries-old politics of neutrality and their need for information in the interest of their country's defense; and that of individuals--professional agents or amateurs, petty smugglers or section chiefs--who formed this international community of information in Switzerland. This work relies on a systematic study of archives relating to counterespionage and the Swiss military justice, as well as numerous documents preserved in the American and British national archives, along with interviews with veterans of the secret war.