This monograph is the fourth in a series on the Army's Professional Military Ethic (PME) that the Chief of Staff of the Army, General George W. Casey, Jr., inaugurated in October 2009. In his series foreword, General Casey encouraged the Army to "think critically about our PME and promote dialogue at all levels as we deepen our understanding of what this time-honored source of strength means to the profession today." In this monograph, Colonel Tony Pfaff explores the ethical challenges facing the Army in an era of persistent conflict dominated by a variety of irregular threats. Pfaff argues that these challenges arise because irregular adversaries change the character of their war from imposing one's will on the enemy to compelling the enemy to accept one's interest. While this shift may seem subtle, Pfaff argues, it suggests a number of important practical and ethical implications for our way of war. Formerly, civilians were largely separable from warfighting, meaning that our strategies of annihilation and attrition were the most effective-and ethical-paths to victory. But now, when combating irregular threats, civilians are no longer separable from warfighting. Consequently, strategies of annihilation and attrition not only undermine a successful resolution of the conflict, but they are unethical. This last point suggests that the Army needs to adapt the PME to account for these changes and to adopt a number of policies and procedures to account for the expanded role irregular conflicts demand Soldiers play. Colonel Pfaff offers a number of practical measures the Army should take to meet this challenge.