The text reviews the nature and causes of MPD, the controversy over its existence, and the meaning of this controversy for the law. It then examines alter personality, the most clinically central aspect of MPD, and considers how well definitions of personhood describe alter personalities. The next section focuses on criminal responsibility, presents a set of rules to govern the responsibility of individuals who have MPD, and contrasts those rules to existing State law. Further sections explore a series of legal questions related to competency to stand trial, civil commitment, and the sentencing of people with MPD. The final section examines other dissociative disorders in the context of criminal responsibility. The analysis concludes that the law's way of assessing criminal responsibility in the case of other mental illnesses and other mental states does not provide a good fit for MPD. Index; chapter notes; appended discussion of assessment, empirical studies, and treatment of MPD; list of cases; and approximately 400 references