This is the fourth volume in the series on the history of the United States Border Patrol covering the period of 2000-2012. This was a critical period in the evolution of the U.S. Border Patrol with the dawning of the new millennium and the aftermath of the terrorist attacks of September 11, 2001. The stand up of the Department of Homeland Security would forever change the operation of the U.S. Border Patrol, taking away or taking over many of the unique and special functions of the Patrol. It also saw the expansion of the politicization of border security and the role the U.S. Border Patrol played in it. Through this period of adversity, the U.S. Border Patrol maintained its leadership role, innovation, and status as the premier border security agency in the world.