In November of 1978, 909 members of the People's Temple perished in Jonestown, Guyana. In March of 1997, 39 followers of the Heaven's Gate cult died in a mass suicide, believing that their souls would join a spacecraft following the comet Hale-Bopp. In the 1960s and 70s, David Berg of the Children of God convinced his followers to abandon their monogamous marriages, encourage pedophilia, and allow their children to be sex trafficked. How do these things happen? This course explores the psychological mechanisms that enable cults to form and to take things to such extremes. What do cults share with other groups (mainstream religions, nations, and everyday social interactions), and what makes them stand apart? In what ways are cults an environment in which many of our psychological tendencies (toward ingroup conformity, heuristic decision making, and rationalization) are magnified? And what do cults reveal about the profound power of our social environment?