According to Janis, groupthink occurs when “members of any small cohesive group tend to maintain esprit de corps by unconsciously developing a number of shared illusions and related norms that interfere with critical thinking and reality testing”. Groupthink can lead to group members making faulty decisions together because they value unanimity over the consideration of all possible alternatives. Using a combination of social psychology, history, and political science, Janis tests his groupthink hypotheses against four major historical events that he labels “major fiascoes”. Then, showing how groups and organizations can stave off groupthink, he describes two historical case studies where decision makers constructed realistic appraisals and properly evaluated the consequences without succumbing to groupthink. The four fiascoes analyzed against groupthink theory are: President Roosevelt’s failure to anticipate the attack on Pear Harbor; President Truman’s decision to invade North Korea; President Kennedy’s Bay of Pigs invasion in Cuba; and President Johnson’s escalation of the Vietnam War. His two case studies of where successful give-and-take deliberation occurred instead of groupthink are the 1962 Cuban missile crisis and how President Truman’s administration evolved the Marshall Plan after World War II. In the final two chapters, Janis describes what type of people and organizations succumb to groupthink and why. He discusses the timing of groupthink as teams of problem solvers move through the various stages of an issue. The last chapter offers tips on how to prevent groupthink. These include adding a devil’s advocate to each team, getting feedback on the group’s current thinking from outside the group and why the team does not want to quickly come to consensus, and giving the decision that is being proposed a chance to be reviewed quickly one last time from a different perspective. This book has value for managers and leaders who seek to understand the pros and cons of group decision making.