The author proposes a definition of harm and applies it to moral, vicarious, posthumous, and prenatal harm. He also relates the concept of harm to associated concepts, such as set back interest, wrongdoing, and violation of rights. He discusses omissions as causes of harm and the controversy over "bad samaritan laws." Using conceptual analysis and references to current legal issues, the volume illuminates the moral implications of rulings on harm and demonstrates how the harm principle must be interpreted if it is to be a plausible guide for legislation. In attempting to address what types of conduct are criminal, the volume examines moral legitimacy and the distinction between criminal statutes that are legitimized by valid moral principles and those that are justified as being legitimate, useful, and economical. Liberty-limiting principles are discussed, with liberty defined as the absence of legal coercion. The concept of liberalism is addressed within the context of criminal law limitations and primary versus derivative crimes. Problems involved in assessing and comparing harm are considered, and public, aggregative, accumulative, and imitative harm is analyzed. References and figures.