The National Commission on Terrorist Attacks Upon the United States, also known as the 9/11 Commission, was an independent, bipartisan commission created by congressional legislation and the signature of President George W. Bush in late 2002. It was chartered to prepare a full and complete account of the circumstances surrounding the September 11, 2001 terrorist attacks on the World Trade Center and the Pentagon, including preparedness for and the immediate response to the attacks. The Commission was also mandated to provide recommendations designed to guard against future attacks.

Chair of the Commission was former New Jersey Governor(1982-1990) Thomas Kean, Vice Chair was former Indiana 9th district Congressman (1965-1998) Lee H. Hamilton. The other commissioners were Richard Ben-Veniste, Fred F. Fielding, Jamie S. Gorelick, Slade Gorton, Bob Kerrey, John F. Lehman, Timothy J. Roemer, and James R. Thompson. A staff of 81 was led by Philip D. Zelikow as Executive Director, Christopher A. Kojm as Deputy Executive Director, and Daniel Marcus as Chief Counsel. Although consisting of five Democrats and five Republicans, Kean and Hamilton agreed from the outset that the process would be nonpartisan and that recommendations would be arrived at by consensus. Hamilton's commitment to this process appears to have been the impetus to compiling his personal historical record contained in the collection.

Because of the scope of the work, staff was divided into 9 teams (later slightly reorganized) to investigate Al Qa'ida and Related Transnational Terrorist Groups; Intelligence Collection, Analysis, Management, Oversight, and Resources; International Counter-Terrorism Policy; Terrorist Financing; Border Security and Foreign Visitors; Law Enforcement and Intelligence Efforts Inside the U.S.; Commercial Aviation and Transportation Security; National Leadership: Immediate Response, Crisis Management, and Continuity of Government; and Emergency Response and Consequence Management: New York City and the Pentagon.

The Commission held an inaugural public hearing March 31-April 1, 2003, providing through testimony an overview of the range of the investigation, then 11 more public hearings in the next 14 months focusing on Congress and Civil Aviation Security; Terrorism, al Qaeda, and the Muslim World; Intelligence and the War on Terrorism; Private/Public Sector Partnerships for Emergency Preparedness; Security and Liberty; Borders, Transportation, and Managing Risk; Counterterrorism Policy; testimony from Condoleezza Rice; Law Enforcement and Intelligence; Emergency Response; and The 9/11 Plot and National Crisis Management.

On July 22, 2004 the Commission released its public report, published in a paperback run of 500,000 by W. W. Norton and priced at $10 in the hope that every American would be able to afford it. On August 21, 2004, staff monographs on Terrorist Financing and on 9/11 and Terrorist Travel were released, accompanied eventually by 17 staff reports on various aspects of the Commission's investigations. The National Archives maintains a website on the 9/11 Commission that provides links to these publications for download, as well as biographical information on the commissioners.

The Commission's mandate expired August 21, 2004. In an effort to maintain pressure on Congress and the Executive branch for implementation of the Commission's recommendations and to build public support, the ten commissioners created the 9/11 Public Discourse Project, which continued through December 31, 2005. Lee Hamilton and his staff continued to document their work during the course of the project, which documentation is contained in the Lee H. Hamilton 9/11 Public Discourse Project Papers, MPP 15.