The earthquake that struck Haiti in 2010 collapsed 100,000 structures, damaged 200,000 more, killed more than 316,000 people, injured 300,000 others, and displaced more than 1 million people. It virtually decapitated the Haitian government, destroying the presidential palace and 14 of 16 government ministries and claiming the lives of numerous government officials and employees and the head of the UN Stabilization Mission in Haiti and his principal deputy. Shortly after the earthquake, surviving Haitian government officials made an urgent request for U.S. assistance. In reply, President Barack Obama promised U.S. support, directing a whole-of-government response led by the U.S. Agency for International Development with significant support from the U.S. Department of Defense through U.S. Southern Command (SOUTHCOM). Selected U.S. military elements began mobilizing immediately, and SOUTHCOM established Joint Task Force-Haiti (JTF-Haiti) to provide U.S. military support to the international response and relief effort through Operation Unified Response (OUR). U.S. Army forces constituted a principal component of JTF-Haiti. Researchers assessed the effectiveness of JTF-Haiti, with the goal of informing the U.S. Army on how to best prepare for and support future humanitarian assistance and disaster relief (HA/DR) operations. This report examines how JTF-Haiti supported the HA/DR effort in Haiti. It focuses on how JTF-Haiti was organized, how it conducted OUR, and how the Army supported that effort. The analysis includes a review of existing authorities and organizations and explains how JTF-Haiti fit into the U.S. whole-of-government approach, as well as the international response.