This Article focuses on habeas petitioners under a conviction from state court seeking federal habeas review. First, Part I will discuss the historical context of the writ of habeas corpus and the development of its purpose and scope. Part I also examines the current status of habeas corpus law, recent legislative efforts to limit its reach, and, specifically, the idea of custody as a prerequisite to habeas relief. Part II explores the evolution of the custody requirement both at the Supreme Court and in lower federal courts. In particular, this section looks at how the meaning of custody has evolved over time from physical custody to more intangible restrictions on liberty. Part III addresses the application of custody jurisprudence to the issue of sex offenders. The Supreme Court has not directly addressed this issue, but several circuit courts have, and Part III addresses the implications of these decisions. Part IV examines sex offender legislation by discussing the particulars of various state statutes and reviewing social science research regarding the effect of the legislative requirements. Finally, Part V looks at the standard applied by courts when discussing sex offender designation as “custody.” This Article argues that the standard has shifted and been analyzed inconsistently. The conclusion contends that, consistent with Supreme Court and lower court precedent on the issue of custody, individuals in many states subject to sex offender laws suffer significant restraints on their liberty and, therefore, meet the jurisdictional requirement for habeas review.