Sept. 11: Terrorists hijack four jetliners and crash them into the World Trade Center, the Pentagon and a Pennsylvania field. The twin towers and Seven World Trade Center collapse.
Sept. 13: Osama bin Laden identified as prime suspect in the attack.
Sept. 14: Nineteen hijackers identified and linked directly to bin Laden.
Sept. 17: Wall Street trading resumes, ending stock market's longest shutdown since the Great Depression. Dow loses 684.81 points, its worst-ever one-day point drop.
Oct. 7: First airstrikes launched in Afghanistan. Bin Laden, in videotaped message, praises God for Sept. 11 attacks.
Oct. 26: President Bush signs anti-terrorism bill giving police unprecedented ability to search, seize, detain and eavesdrop in pursuit of possible terrorists.
Nov. 25: First wave of Marines lands near Taliban stronghold of Kandahar.
Dec. 22: Hamid Karzai and his transitional government sworn in to lead Afghanistan.
Feb. 14: Leaders of House and Senate intelligence committees announce joint inquiry of intelligence community's failure to prevent the attacks.
Sept. 18: Investigator for joint inquiry testifies that intelligence agencies disregarded many warnings that terrorists might use planes as bombs.
Nov. 25: Bush signs legislation creating Department of Homeland Security.
Nov. 27: Bush signs bill establishing independent commission to investigate the Sept. 11 attacks.
Dec. 11: Congressional inquiry issues final report on intelligence failures leading up to terrorist attacks. Key recommendations include creating Cabinet-level director of national intelligence.
Dec. 13: WTC death toll drops to 2,792, one of several drops since the first anniversary of the attacks.
Jan. 1: Thousands of newly hired government workers begin screening every checked bag at the nation's commercial airports for explosives.
Jan. 27: The independent 9/11 commission, headed by ex-New Jersey Gov. Thomas H. Kean, launches its 16-month investigation.
Feb. 19: Moroccan student Mounir el Motassadeq receives the maximum 15-year sentence in Germany for helping Sept. 11 hijackers. It was the first conviction tied to the terror plot and was later overturned. Motassadeq was subsequently convicted of belonging to a terrorist organization and sentenced to seven years. He was acquitted of more than 3,000 counts of being an accessory to murder. He is released from prison in February 2006 when a German federal court rules he shouldn't be jailed with appeals still pending. A hearing on his appeal is scheduled for Oct. 12.
Feb. 27: Architect Daniel Libeskind's Freedom Tower plan, including a 1,776-foot spire and sunken memorial, chosen for rebuilding trade center.
March 3: Design announced for Pentagon memorial, with 184 benches each placed over an individual reflecting pool inscribed with a victim's name.
March 19: Bush announces a U.S.-led coalition has begun "military operations to disarm Iraq, to free its people and to defend the world from grave danger."
March 31-April 1: The 9/11 commission holds first public hearings, a half mile from ground zero.
May 7: Federal investigators report that fireproofing on the WTC's steel floor supports was never tested and might not have met city building code.
Aug. 28: The Port Authority releases 2,000 pages of transcripts from emergency calls and radio transmissions following attacks.
Nov. 6: Firehouse across from World Trade Center re-opens.
Jan. 23: The New York City Medical Examiner places final death toll from trade center attacks at 2,749.
June 16-17: 9/11 Commission concludes 20 months of investigation with a preliminary report that fails to find "credible evidence" of collaboration between Iraq and al-Qaida on attacks.
July 22: 9/11 Commission delivers final report to President Bush; its key findings include the failure of the Bush and Clinton administrations to make anti-terrorism a top priority.
Dec. 17: Bush signs Intelligence Reform Act, a historic overhaul of the national intelligence system.
March 24: Court ruling orders New York and its Fire Department to release tapes and transcripts of post-attack interviews with city firefighters, along with 911 calls from department personnel. Nearly nine hours of edited transcripts and recordings were released in March 2006.
April 22: Zacarias Moussaoui, the only person indicted in the U.S. for the attacks, pleads guilty to conspiring with the Sept. 11 hijackers. He is sentenced to six life terms to run as two consecutive life sentences in May 2006.
July 25: Former 9/11 Commission members give government "mixed grade" in following through on the panel's year-old recommendations.
Sept. 7: A design is chosen for the Flight 93 National Memorial in Pennsylvania. The design pays tribute to the heroic struggle by passengers who thwarted an attack on the nation's capital.
Jan. 9: The Dow Jones industrial average closes above 11,000 for the first time since before the attacks.
March 28: Construction workers near the World Trade Center site discover more bone fragments and human remains. In September, hundreds more fragments are found on the roof of the former Deutsche Bank building.
May 16: The Pentagon releases the first video images of American Airlines Flight 77 crashing into the military headquarters.
May 23: Opening of 7 World Trade Center, the third building to fall on Sept. 11 and the first to be rebuilt.
July 31: NATO troops take command of military operations in southern Afghanistan from the U.S.-led coalition.