- Feb 4 Mark Zuckerberg launches Facebook from his Harvard dormitory room
- Apr 8 Darfur conflict: The Humanitarian Ceasefire Agreement is signed by the Sudanese government and two rebel groups
- May 17 Massachusetts becomes the first U.S. state to legalize same-sex marriage
- May 21 Stanislav Petrov awarded World Citizen Award for averting a potential nuclear war in 1983 after correctly guessing Russian early warning system at fault
- May 26 The United States Army veteran Terry Nichols is found guilty of 161 state murder charges for helping carry out the Oklahoma City bombing.
- Jul 5 First Indonesian presidential election by the people - first round (eventually won by Susilo Bambang Yudhoyono)
- Nov 11 Yasser Arafat's death through unidentified causes confirmed by Palestine Liberation Organization, Mahmoud Abbas elected PLO chairman minutes later.
- Dec 8 The Cuzco Declaration is signed in Cuzco, Peru, establishing the South American Community of Nations.
- Dec 26 9.3 magnitude earthquake creates a tsunami causing devastation in Sri Lanka, India, Indonesia, Thailand, Malaysia, the Maldives and edges of the Indian Ocean, killing 230,000 people
The Republic of Ireland becomes the first country in the world to ban smoking in all work places, including bars and restaurants.
On March 29, 2004
Google introduces Gmail: the launch is met with scepticism on account of the launch date.
On April 1, 2004