- May 1 130th Kentucky Derby: Stewart Elliott wins aboard Smarty Jones. North American wagering records smashed ($142m on 12-race card)
- May 1 Cyprus, Czech Republic, Estonia, Hungary, Latvia, Lithuania, Malta, Poland, Slovakia, and Slovenia join the European Union, celebrated at the residence of the Irish President in Dublin.
Baseball Record
May 1 Giants outfielder Barry Bonds sets MLB record for being intentionally walked 4 times in a 9-inning game during 6-3 defeat of Florida in SF
- May 2 Yelwa massacre of more than 630 nomad Muslims by Christians in Nigeria
Television Finale
May 6 TV sitcom "Friends" airs season finale in 10th and final season in US (52.5 million viewers)
- May 9 Chechen president Akhmad Kadyrov is killed in a land mine bomb blast under a VIP stage during a World War II memorial victory parade in Grozny, Chechnya
Laureus Awards
May 10 Laureus World Sports Awards, Cultural Centre of Belém, Lisbon, Portugal: Sportsman: Michael Schumacher; Sportswoman: Annika Sörenstam; Team: England Men's National Rugby Union team
Shrek 2
May 15 "Shrek 2" directed Andrew Adamson and Kelly Asbury, with voices by Mike Myers, Eddie Murphy and Cameron Diaz premieres at the Cannes Film Festival
- May 15 129th Preakness: Stewart Elliott aboard Smarty Jones wins in 1:55.59
- May 15 49th Eurovision Song Contest: Ruslana for Ukraine wins singing "Wild Dances" in Istanbul
- May 16 Day of Mourning at Bykivnia forest, just outside of Kyiv, Ukraine where during 1930s and early 1940s communist bolsheviks executed over 100,000 Ukrainian civilians
- May 17 Massachusetts becomes the first U.S. state to legalize same-sex marriage
- May 18 Arizona Diamondbacks' Randy Johnson becomes 16th pitcher to throw a perfect game (2-0 vs Atlanta)
- May 19 NHL Western Conference Final: Calgary Flames beat San Jose Sharks, 4 games to 2
The Notebook
May 20 Cult romantic film "The Notebook" premieres at the Seattle Film Festival, starring Rachel McAdams and Ryan Gosling and directed by Nick Cassavetes
- May 21 Sherpa Pemba Dorjie climbs Mount Everest in 8 hours 10 minutes, breaking his rival Sherpa Lakpa Gelu's record from the previous year.
- 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
57th Cannes Film Festival
May 22 57th Cannes Film Festival: "Fahrenheit 9/11", directed by Michael Moore wins the Palme d'Or. First documentary to win.
FA Cup Final
May 22 English FA Cup Final, Millennium Stadium, Cardiff (71,350): Manchester United beats Millwall, 3-0; Ruud van Nistelrooy scores 2 and Cristiano Ronaldo 1 in Red Devils' 11th title win
PM Manmohan Singh
May 22 Manmohan Singh becomes the 13th Prime Minister of India
- May 22 NHL Eastern Conference Final: Tampa Bay Lightning beat Philadelphia Flyers, 4 games to 3
- May 22 Super Rugby Final, Canberra: ACT Brumbies claim their 2nd title with a 47-38 win over Canterbury Crusaders; Brumbies wingers Mark Gerrard (3) and Joe Roff (2) combine for 5 tries
- May 22 The U.S. town of Hallam, Nebraska, is wiped out by a powerful F4 tornado that broke a width record at an astounding 2.5 miles wide. It also kills one local resident.
- May 23 Part of Paris Charles de Gaulle Airport's Terminal 2E collapses, killing four people and injuring three others.
- May 24 North Korea bans mobile phones.
- May 26 12th UEFA Champions League Final: Porto beats AS Monaco 3-0 at Gelsenkirchen
Academy of Country Music Awards
May 26 39th Academy of Country Music Awards: Toby Keith & Martina McBride win
- May 26 The New York Times publishes admission of journalistic failings, claims its flawed reporting and lack of skeptism during buildup to 2003 Iraq War helped promote belief that Iraq possessed large stockpiles of weapons of mass destruction.
- 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.
- May 28 The Iraqi Governing Council chooses Ayad Allawi, a longtime anti-Saddam Hussein exile, to become Prime Minister of Iraq's interim government
- May 29 The Al-Khobar massacres in Saudi Arabia kill 22
- May 29 The World War II Memorial is dedicated in Washington, D.C.
Indy 500
May 30 Indianapolis 500: Buddy Rice wins from pole for team owners Bobby Rahal and David Letterman in a rain shortened race (450 miles - 180 of 200 scheduled laps)
Harry Potter and the Prisoner of Azkaban
May 31 "Harry Potter and the Prisoner of Azkaban", the 3rd film based on the books by J. K. Rowling is released in UK cinemas
- May 31 British children's cartoon "Peppa Pig" created by Astley Baker Davies premieres on Channel 5
Senior PGA Championship
May 31 Senior PGA Championship, Valhalla GC: Hale Irwin wins his 4th title in the event by 1 stroke ahead of runner-up Jay Haas