2003 (MMIII) was a common year starting on Wednesday (dominical letter E) of the Gregorian calendar, the 2003rd year of the Common Era (CE) and Anno Domini (AD) designations, the third year of the 3rd millennium, the third year of the 21st century, and the fourth year of the 2000s decade.
2003 was designated the:
- January 22 – The last signal from NASA's Pioneer 10 spacecraft is received, a few 7.6 billion miles from Earth.
- January 30 – Belgium legally recognises same-sex marriage, fitting the second country in the world to do so.
- February 1 – At the conclusion of the STS-107 mission, the Space Shuttle Columbia disintegrates throughout reentry over Texas, killing all 7 astronauts on board.
- February 4 – The leaders of the Federal Republic of Yugoslavia reconstitute the country into a loose state-union between Montenegro and Serbia, marking an end to the 85 year old Yugoslav state.
- February 15 – Millions of people worldwide take part in massive anti-war protests before the United States and its allies invade Iraq.
- February 20 – The Station nightclub fire in West Warwick, Rhode Island kills 100 people and injures 230.
- February 26 – The War in Darfur begins after rebel groups rise up against the Sudanese government.
- February 27 – Former Bosnian Serb leader Biljana Plavšić is sentenced by the U.N. ICTY to 11 years in prison for war crimes committed throughout the Bosnian War.
- March 8 – Malta approves joining the European Union in a referendum.
- March 12
- March 20 – The Iraq War begins with the invasion of Iraq by the U.S. and allied forces.
- March 23 – Slovenia approves joining the European Union and NATO in a referendum.
- April 9 – Iraq War: U.S. forces seize control of Baghdad, ending the regime of Saddam Hussein.
- April 12 – Hungary approves joining the European Union in a referendum.
- April 14 – The Human Genome Project is completed, with 99 percent of the human genome sequenced to 99.99% accuracy.
- April 29 – The United States announces the withdrawal of troops stationed in Saudi Arabia, and the redeployment of a few at the Al Udeid Air Base in Qatar.
- May 1 – U.S President George W. Bush gives a speech announcing the end of major combat operations in the Iraq War.
- May 11
- May 12 – In Riyadh, Saudi Arabia, over 30 people are killed in multiple bombings at a housing compound, mostly foreign expatriates.
- May 17 – Slovakia approves joining the European Union in a referendum.
- May 19 – Insurgency in Aceh: The Indonesian military begins a massive military operation in Aceh against Free Aceh Movement separatists.
- May 21 – A 6.8 magnitude earthquake strikes northern Algeria with a maximum Mercalli intensity of X (Extreme). The shock generated a destructive tsunami in the Mediterranean Sea and left over a thousand people dead and 7,000 more injured.
- May 23 – Dewey, the first deer cloned by scientists at Texas A&M University, is born.
- May 28 – Prometea, the first horse cloned by Italian scientists, is born.
- June 8 – Poland approves joining the European Union in a referendum.
- June 14 – The Czech Republic approves joining the European Union in a referendum.
- June 26 – The Supreme Court of the United States, in a landmark ruling, strikes down sodomy laws and rules them to be unconstitutional, effectively legalising homosexual sodomy nationwide.
- June 30 – Warring parties in the Democratic Republic of the Congo sign a peace accord, bringing an end to the Second Congo War, which left millions dead.
- July 1 – 500,000 people in Hong Kong march to protest Hong Kong Basic Law Article 23, which controversially redefines treason.
- July 5 – Severe acute respiratory syndrome is declared to be contained by the World Health Organization.
- July 6 – The 70-meter Eupatoria Planetary Radar sends a METI message Cosmic Call 2 to 5 stars: Hip 4872, HD 245409, 55 Cancri, HD 10307 and 47 Ursae Majoris, that will arrive at these stars in 2036, 2040, May 2044, September 2044 and 2049 respectively.
- July 8 – Sudan Airways Flight 139, with 117 people on board, crashes in Sudan; the only survivor is a 2-year-old child.
- July 18 – The Convention on the Future of Europe finishes its work and proposes the first European Constitution.
- July 22 – Uday and Qusay Hussein, sons of Saddam Hussein, are killed by the U.S. military in a shootout at a house in Mosul.
- July 24 – The Regional Assistance Mission to the Solomon Islands, led by Australia, begins after ethnic violence engulfs the island country.
- August 11
- August 25 – The Spitzer Space Telescope is launched from Cape Canaveral, Florida.
- August 27
- September 3 – The Hubble Space Telescope starts the Hubble Ultra-Deep Field, making 800 exposures, until January 16, 2004.
- September 4 – Europe's busiest shopping centre, the Bull Ring in Birmingham, is officially opened.
- September 14 – Estonia approves joining the European Union in a referendum.
- September 15 – ELN rebels kidnap eight foreign tourists at Ciudad Perdida, Colombia, being freed 100 days later following negotiations with the Colombian government.
- September 20 – Latvia approves joining the European Union in a referendum.
- September 27 – SMART-1, a European Space Agency satellite and Europe's first mission to the moon, is launched.
- October 5 – Israeli warplanes strike alleged Islamic jihad bases inside Syrian territory, the first Israeli attack on the country after the 1973 Yom Kippur War.
- October 15 – China launches Shenzhou 5, their first manned spaceflight.
- October 24 – The Concorde makes its last commercial flight, bringing the era of airliner supersonic travel to a close.
- November 12 – A suicide bombing at an Italian military police headquarters in Nasiriyah, Iraq, kills 17 Italian military police officers and nine Iraqi civilians.
- November 18 – The Massachusetts Supreme Judicial Court declares in a landmark ruling that only opposite-sex couples having the right to marry is unconstitutional, paving the way for Massachusetts to become the first U.S. State to legalise same-sex marriage.
- November 23 – Georgian President Eduard Shevardnadze resigns after widespread protests engulf the country following a disputed parliamentary election.
- December 13 – Saddam Hussein, former President of Iraq, is captured in the small town of Ad-Dawr by the U.S. Army.
- December 19 – Libya agrees to eliminate all of its materials, equipment, and programmes aimed at producing weapons of mass destruction.
- December 23 – The World Tourism Organization becomes a specialised agency of the United Nations.
- December 26 – A 6.6 magnitude earthquake shakes southeastern Iran with a maximum Mercalli intensity of IX (Violent), killing tens of thousands of people.
- January 6 – MattyBRaps, American rapper
- August 18 – Max Charles, American child actor
- August 20 – Prince Gabriel of Belgium
- August 28 – Quvenzhané Wallis, American child actress
- November 8 – Lady Louise Windsor, daughter of Prince Edward, Earl of Wessex and Sophie, Countess of Wessex
- December 7 – Princess Catharina-Amalia of the Netherlands, daughter of Willem-Alexander of the Netherlands and Queen Maxima
- January 11 – Maurice Pialat, French actor and director (b. 1925)
- January 12
- January 17 – Richard Crenna, American actor (b. 1926)
- January 23 – Nell Carter, American singer and actress (b. 1948)
- January 24 – Gianni Agnelli, Italian auto executive (b. 1921)
- January 26
- January 27 – Henryk Jabłoński, fifth President of the Polish People's Republic (b. 1909)
- February 1
- Michael P. Anderson, American astronaut (b. 1959)
- David M. Brown, American astronaut (b. 1956)
- Kalpana Chawla, American astronaut (b. 1962)
- Laurel Clark, American astronaut (b. 1961)
- Rick Husband, American astronaut (b. 1957)
- William McCool, American astronaut (b. 1961)
- Ilan Ramon, Israeli fighter pilot and astronaut (b. 1954)
- February 2 – Lou Harrison, American composer (b. 1917)
- February 10 – Curt Hennig, American professional wrestler (b. 1958)
- February 20 – Maurice Blanchot, French philosopher and writer (b. 1907)
- February 27
- February 28 – Fidel Sánchez Hernández, 45th President of El Salvador (b. 1917)
- March 2 – Hank Ballard, American musician (b. 1927)
- March 9 – Bernard Dowiyogo, second President of Nauru (b. 1946)
- March 12
- March 22 – Milton George Henschel, American Jehovah's Witnesses leader (b. 1920)
- March 26 – Daniel Patrick Moynihan, American politician (b. 1927)
- March 29 – Carlo Urbani, Italian physician (b. 1956)
- March 30 – Michael Jeter, American actor (b. 1952)
- April 1 – Leslie Cheung, Hong Kong singer and actor (b. 1956)
- April 2 – Edwin Starr, American soul singer (b. 1942)
- April 9 – Jorge Oteiza, Spanish painter (b. 1908)
- April 17 – Robert Atkins, American nutritionist (b. 1930)
- April 20
- April 21 – Nina Simone, American singer (b. 1933)
- May 11 – Noel Redding, English musician (b. 1946)
- May 12 – Prince Sadruddin Aga Khan, French U.N. High Commissioner for Refugees (b. 1933)
- May 14
- May 15
- May 24 – Rachel Kempson, English actress (b. 1910)
- May 27 – Luciano Berio, Italian composer (b. 1925)
- May 28
- June 10
- June 12 – Gregory Peck, American actor (b. 1916)
- June 15
- June 21 – Leon Uris, American writer (b. 1924)
- June 22 – Vasil Bykaŭ, Belarusian novelist (b. 1924)
- June 26
- June 29 – Katharine Hepburn, American actress (b. 1907)
- June 30 – Buddy Hackett, American comedian and actor (b. 1924)
- July 1
- July 4 – Barry White, American singer (b. 1944)
- July 6 – Buddy Ebsen, American actor (b. 1908)
- July 12 – Benny Carter, American musician (b. 1907)
- July 13 – Compay Segundo, Cuban musician (Buena Vista Social Club) (b. 1907)
- July 15 – Roberto Bolaño, Chilean writer (b. 1953)
- July 16
- July 17 – Rosalyn Tureck, American pianist and harpsichordist (b. 1914)
- July 22
- July 25 – John Schlesinger, English film director (b. 1926)
- July 27 – Bob Hope, English-American comedian and actor (b. 1903)
- July 30 – Sam Phillips, American record producer (b. 1923)
- August 1 – Marie Trintignant, French actress (b. 1962)
- August 4 – Frederick Chapman Robbins, American paediatrician and virologist, Nobel Prize laureate (b. 1916)
- August 9 – Gregory Hines, American dancer and actor (b. 1946)
- August 11 – Armand Borel, Swiss mathematician (b. 1923)
- August 14 – Helmut Rahn, German footballer (b. 1929)
- August 16 – Idi Amin, third President of Uganda (b. c. 1923–28)
- August 19
- August 29 – Vladimír Vašíček, Czech painter (b. 1919)
- August 30 – Charles Bronson, American actor (b. 1921)
- September 7 – Warren Zevon, American singer (b. 1947)
- September 8 – Leni Riefenstahl, German film director (b. 1902)
- September 9 – Edward Teller, Hungarian-American physicist (b. 1908)
- September 11
- September 12 – Johnny Cash, American singer-songwriter and actor (b. 1932)
- September 24 – Edward Said, Palestinian-American literary critic (b. 1935)
- September 25 – Franco Modigliani, Italian-American economist, Nobel Prize laureate (b. 1918)
- September 26
- September 27 – Donald O'Connor, American actor, singer, and dancer (b. 1925)
- September 28
- September 30 – Robert Kardashian, Armenian-American attorney and businessman (b. 1944)
- October 3 – William Steig, American cartoonist (b. 1907)
- October 5
- October 10 – Eugene Istomin, American pianist (b. 1925)
- October 13 – Bertram Brockhouse, Canadian physicist, Nobel Prize laureate (b. 1918)
- October 16
- October 19
- October 20 – Jack Elam, American actor (b. 1918)
- October 21 – Elliott Smith, American musician (b. 1969)
- October 23 – Soong Mei-ling, Chinese wife of Chiang Kai-shek (b. 1897)
- October 24 – Veikko Hakulinen, Finnish cross-country skier (b. 1925)
- October 27 – Rod Roddy, American television announcer (b. 1937)
- October 29
- November 6
- November 9 – Art Carney, American actor (b. 1918)
- November 10 – Canaan Banana, first President of Zimbabwe (b. 1936)
- November 12 – Jonathan Brandis, American actor (b. 1976)
- November 18 – Michael Kamen, American composer (b. 1948)
- November 20 – David Dacko, first President of the Central African Republic (b. 1930)
- November 24 – Warren Spahn, American baseball player (b. 1921)
- November 30 – Gertrude Ederle, American swimmer (b. 1905)
- December 3 – David Hemmings, English actor (b. 1941)
- December 6
- December 8 – Rubén González, Cuban pianist (Buena Vista Social Club) (b. 1919)
- December 11 – Ahmadou Kourouma, Ivorian writer (b. 1927)
- December 12 – Heydar Aliyev, third President of Azerbaijan (b. 1923)
- December 14 – Jeanne Crain, American actress (b. 1925)
- December 19 – Hope Lange, American actress (b. 1933)
- December 27 – Alan Bates, English actor (b. 1934)
- December 30 – Anita Mui, Hong Kong singer (b. 1963)
Nobel Prize winners
- Chemistry – Peter Agre, Roderick MacKinnon
- Economics – Robert F. Engle, Clive W. J. Granger
- Literature – John Maxwell Coetzee
- Peace – Shirin Ebadi
- Physics – Alexei Alexeyevich Abrikosov, Vitaly Lazarevich Ginzburg, Anthony James Leggett
- Physiology or Medicine – Paul Lauterbur, Peter Mansfield