Why do groups of talented and experienced individuals make disastrously bad collective judgments, such as the Kennedy administration's flawed decision to proceed with the Bay of Pigs invasion in 1961? In his pioneering research on collective decision making, Irving Janis introduced the concept of groupthink-a deliberately Orwellian neologism-to describe such occurrences. Now, in the first book-length study of groupthink since Janis's work, Paul 't Hart has provided a rigorous and systematic version of this influential theory which opens several new avenues for research.