Most studies of the coup d’état in Iran in August 1953—a coup backed by U.S. and British intelligence agencies—attribute it at least partly to U.S. concerns about the threat of a Communist takeover in Iran. This article examines the evidence available to U.S. officials about the nature of the Communist threat in Iran prior to the coup, in the form of reports, analyses, and policy papers written on this subject at the time by U.S. officials. The documentation reveals that U.S. policymakers did not have compelling evidence that the threat of a Communist takeover was increasing substantially in the months before the coup. Rather, the Eisenhower administration interpreted the available evidence in a more alarming manner than the Truman administration had. The coup the administration undertook in response was therefore premature, at best.