The First Additional Protocol to the Geneva Conventions ("AP I") is central to the modern law of war, widely referred to as international humanitarian law outside the United States. It updates the Geneva Conventions for protection of war victims and combines them with new or updated rules governing hostilities and the use of weapons found in the Hague Regulations Respecting the Laws and Customs of War. Due to its comprehensive nature and adoption by a majority of States, AP I is frequently cited as the source for law of war rules by attorneys and others interested in protecting humanitarian interests. The challenge for United States attorneys, however, is that their country is not a party to AP I and has been a persistent objector to many of its new rules.While the United States signed the First Additional Protocol to the Geneva Conventions in 1977, it determined, after 10 years of analysis, that it would not ratify the protocol. President Reagan called AP I "fundamentally and irreconcilably flawed."1 Yet, as will be detailed throughout this guide, United States officials have declared that aspects of AP I are customary international law. Forty years after signing AP I, and 30 years after rejecting it, the United States has never presented a comprehensive, systematic, official position on the protocol. Officials from the United States Departments of Defense and State have taken positions on particular portions of it. This guide attempts to bring those sources together in one location.