| National Physical Fitness and Sports Month | May |
| Sudoku First Published as Number Place in Dell Puzzle Magazine | May, 1979 |
| May Day | May 1, 2008 |
| Mother Goose Day | May 1, 2008 |
| Whale Awareness Day (in Massachusetts) | May 1, 2008 |
| Holocaust Day | May 2, 2008 |
| Space Day | May 2, 2008 |
Elizabeth Jane Cochran's, Known as Nellie Bly, Birthday | May 5, 1864 |
| Cinco de Mayo | May 5, 2008 |
| Cartoonist Day | May 5, 2008 |
| Eta Aquarids Meteor Shower | May 5, 2008 |
| International Astronomy Week | May 5-11, 2008 |
| SAT Registration Deadline | May 6, 2008 |
| Beethoven's Ninth Symphony Premiere | May 7, 1824 |
| Central and Union Pacific Railroads Meet | May 10, 1869 |
| National Windmill Day (Holland) | May 10, 2008 |
| International Migratory Bird Day | May 10, 2008 |
| Richard Feynman's Birthday | May 11, 1918 |
| Mother's Day | May 11, 2008 |
| Mother's Day (postcard) | May 11, 2008 |
| Edward Lear's Birthday (Celebrated as Limerick Day) | May 12, 1812 |
| Edward Lear's Limericks | May 12, 1812 |
| Start of California Gold Rush | May 12, 1848 |
| Children's Book Week | May 12-,18 2008 |
| First permanent British colony Established in Jamestown, Virginia | May 14, 1607 |
| Lewis & Clark Leave St. Louis | May 14, 1804 |
| Major Lassen Peak Volcanic Eruption | May 14, 1915 |
| Jumping Frog Jubilee in Angels Camp, CA | May 14-18, 2008 |
| L. Frank Baum's Birthday | May 15, 1856 |
| Discovery of Largest Prime Number Known to Man | May 15, 2004 |
| Sue Debuts at Field Museum | May 17, 2000 |
| Karol Wojtyla Birthday (Pope John Paul II) | May 18, 1920 |
| Major Mount St. Helens Volcanic Eruption | May 18, 1980 |
Circus Day, Anniversary of First Ringling Brothers Performance | May 19, 1884 |
Premiere of Star Wars: Episode I | May 19, 1999 |
| National Backyard Games Week | May 19-26, 2008 |
Charles Lindbergh Flies Historic Solo Nonstop Transatlantic Flight | May 20-21, 1927 |
| Amelia Earhart's Atlantic Crossing | May 20, 1932 |
| Weights and Measures Day | May 20, 2008 |
| Most Powerful Earthquake of the 20th Century Struck Chile | May 22, 1960 |
| Jerusalem Day | May 22, 2008 |
| Hurricane Preparedness Week | May 25 - 31, 2008 |
| Memorial Day | May 26, 2008 |
| World Turtle Day | May 23, 2008 |
| Cellophane Tape Patented | May 27, 1930 |
| Golden Gate Bridge Opened | May 27, 1937 |
| John F. Kennedy's Birthday | May 29, 1917 |
| First Daily American Newspaper Published | May 30, 1783 |
| Walt Whitman's Birthday | May 31, 1819 |
| National Spelling Bee Week | May 25-31, 2008 |
| Mark Felt Reveals Himself as Watergate's Deep Throat | May 31, 2005 |
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