Civil wars continue to be a frequent and debilitating phenomenon in international politics. Of the approximately 200 countries in the world, there are currently 30 civil wars underway, including several in which the U.S. military is directly and deeply enmeshed. In the twelve essays in this issue, the authors explore causative factors of civil war, the connection of intrastate strife and transnational terrorism, the limited successes and failed ambitions of intervening powers in the recent past, and the many direct and indirect consequences associated with weak states and civil wars, including the dangers posed by pandemics, mass migrations of people, and great-power proxy warfare.