The Aspen Strategy Group's Policy Books is an annual series of pieces written by contemporary thought leaders on the most pressing U.S. foreign policy and national security issues. This edition is a collection of papers commissioned for the 2015 Aspen Strategy Group Summer Workshop, in Aspen, Colorado. The summer workshop convened a nonpartisan group of foreign policy experts, academics, journalists, and business leaders. The group's policy discussions were guided by the papers in this volume, which evaluate the roots of extremism, the rise of the Islamic State, and the costs and risks associated with intensifying U.S. engagement in Iraq and Syria.