This article briefly discusses the historical development of the constructs of paraphilia and psychopathy. An overview of recent developments in the assessment of these constructs for legal purposes is also provided. The historical, clinical, legal, and ethical obligations of clinicians who work with persons suffering from paraphilias and co-morbid psychopathy is then reviewed. An emphasis of the current article is integrating recent developments in the construct of psychopathy into a discussion of sex offender risk assessment and treatment. The co-morbidity of psychopathy and paraphilias as factors in predicting risk of recidivism is reviewed. The need for practitioners to remain cognizant of language requirements in both legal and clinical contexts is addressed. Finally, this article reviews the legal history of sex offender legislation and its evolution into current United States Supreme Court jurisprudence.