Under the Constitution, the war powers are divided between Congress and the President. Among other relevant grants, Congress has the power to declare war and raise and support the armed forces) while the President is Commander-in-Chief. It is generally agreed that the Commander-in-Chief role gives the President power to utilize the armed forces to repel attacks against the United States, but there has long been controversy over whether he is constitutionally authorized to send forces into hostile situations abroad without a declaration of war or other congressional authorization. This book discusses and assesses the War Powers Resolution and its application since enactment in 1973, providing detailed background on various cases in which it was used, as well as cases in which issues of its applicability were raised. It focuses on the several proposals for a new AUMF specifically targeting the Islamic State made during the 113th and 114th Congresses. It includes a brief review of existing authorities and AUMFs, as well as a discussion of issues related to various provisions included in existing and proposed AUMFs that both authorize and limit presidential use of military force. Appendices provide a comparative analysis of similar provisions in new AUMFs proposed in the 113th and 114th Congresses.