Fifty years ago this month, we published an essay by Yale psychology professor Irving Janis about "groupthink,” a compulsion by decision-makers to have each other's approval, even at the cost of critical thinking. Janis looked at three American foreign policy decisions through this lens: pre-World War II complacency about the fleet in Pearl Harbor, the Bay of Pigs invasion, and escalation in Vietnam. The article is still one of our most requested for reprint.