2001 (MMI) was a common year starting on Monday of the Gregorian calendar, the 2001st year of the Common Era (CE) and Anno Domini (AD) designations, the 1st year of the 3rd millennium and the 21st century, and the 2nd year of the 2000s decade.

2001 was dominated by the September 11 attacks against the United States by Al-Qaeda, which killed 2,977 people and instigated the global war on terror. The United States led a multi-national coalition in an invasion of Afghanistan after the Taliban government did not extradite Al-Qaeda leader Osama bin Laden.

Internal conflicts, political or otherwise, caused shifts in leadership in multiple countries, which included the assassination of Laurent-Désiré Kabila in the Democratic Republic of the Congo, the Second EDSA Revolution in the Philippines, the massacre of the royal family by the crown prince in Nepal, and civil unrest in Argentina. Other notable political events were an escalation in the Israeli–Palestinian conflict, the storming of the Indonesian parliament, the Hainan Island incident between China and the United States, an insurgency in Macedonia, and a terrorist attack on the Parliament of India that began the 2001–2002 India–Pakistan standoff.

Space milestones in 2001 were numerous, the most notable being the first spacecraft landing on an asteroid, the deorbit of the Russian station Mir , American entrepreneur Dennis Tito becoming the first space tourist, the discovery of 28978 Ixion in the Kuiper belt, a flyby of Io by the U.S. Galileo probe, and the first discovery of an atmosphere on an exoplanet. In addition, the year witnessed the first sequence of the human genome, the first self-contained artificial heart, and the first clone of a human embryo.

2001 was designated as International Year of Volunteers by the United Nations.