Is the targeted killing of United States citizens legal? There are two competing models which address the legality of targeted killings: the law-enforcement model and the armed-conflict model. This book examines arguments for and against each model. Using the Issue, Rule, Analysis and Conclusion methodology for legal analysis, it analyzes the facts of the case of Anwar al-Awlaki under each model, and based on judicial balancing tests, concludes that neither serves both the interests of protecting constitutional rights and combating terrorism. This book will show that while the law-enforcement model offers the greatest protection for the constitutional rights of U.S. citizens, it fails to adequately address the threat of terrorism, and that while the armed-conflict model effectively addresses threats, it risks violating constitutional rights. This book considers proposals for mitigating violations of constitutional rights under the armed-conflict model and ultimately concludes that a third model, based on a system of national security courts, used to determine whether U.S. citizens performed continuous combat functions within organized armed groups, based on the preponderance of evidence, provides decision makers with the best basis from which to determine the permissibility of conducting targeted killings against U.S. citizens. As proposed, this national security model avoids the restrictions of the political question doctrine and allows for adequate protection of due process rights for U.S. citizens.