A taboo is an "unthinkable"action. Even the thought of violating a taboo triggers a punishment. We consider a model in which taboos are part of the definition of one's identity. Deliberating over breaking the taboo changes the individual's choice set, and provides information on possible private benefits. The strength of the taboo is determined by the number of individuals that obey it. We analyze the relationship between social heterogeneity and taboos' strength. We then examine societies in which individuals choose among several identities characterized by different taboos. We characterize the conditions that give rise to a multi-identity society.