The U.S. withdrawal from Afghanistan is understood to encompass the U.S. military retrograde, beginning with the "e;Go to Zero"e; order officially announced by President Biden on April 14, 2021, through the noncombatant evacuation operation (NEO) ordered by President Biden on August 15, 2021, as well as related planning by the White House, U.S. Department of State, and other federal agencies and their decision-making processes. The withdrawal culminated in the Abbey Gate terrorist attack on August 26, 2021, which killed 13 U.S. servicemembers, wounding another 45, and killed more than 170 Afghan civilians. The withdrawal concluded on August 30, 2021, when the last U.S. military aircraft left Afghanistan. This book presents the investigation into the Biden-Harris administration's withdrawal from Afghanistan in 2021.