| 55561 | May.15 | Event | 1963 – Project Mercury: The launch of the final Mercury mission, Mercury-Atlas 9 with astronaut Gordon Cooper on board. He becomes the first American to spend more than a day in space, and the last American to go into space alone. |
| 55562 | May.15 | Event | 1966 – After a policy dispute, Prime Minister Nguyễn Cao Kỳ of South Vietnam's ruling junta launches a military attack on the forces of General Tôn Thất Đính, forcing him to abandon his command. |
| 55563 | May.15 | Event | 1969 – People's Park: California Governor Ronald Reagan has an impromptu student park owned by University of California at Berkeley fenced off from student anti-war protestors, sparking a riot called Bloody Thursday. |
| 55564 | May.15 | Event | 1970 – President Richard Nixon appoints Anna Mae Hays and Elizabeth P. Hoisington the first female United States Army Generals. |
| 55565 | May.15 | Event | 1970 – Philip Lafayette Gibbs and James Earl Green are killed at Jackson State University by police during student protests. |
| 55566 | May.15 | Event | 1972 – Okinawa, under U.S. military governance since its conquest in 1945, reverts to Japanese control. |
| 55567 | May.15 | Event | 1972 – In Laurel, Maryland, Arthur Bremer shoots and paralyzes Alabama Governor George Wallace while he is campaigning to become President. |
| 55568 | May.15 | Event | 1974 – Ma'alot massacre: Members of the Democratic Front for the Liberation of Palestine attack and take hostages at an Israeli school a total of 31 people are killed, including 22 schoolchildren. |
| 55569 | May.15 | Event | 1986 – Elio de Angelis, was killed while testing the Brabham BT55 at the Paul Ricard circuit at Le Castellet. |
| 55570 | May.15 | Event | 1987 – The Soviet Union launches the Polyus prototype orbital weapons platform. It fails to reach orbit. |
| 55571 | May.15 | Event | 1988 – Soviet war in Afghanistan: After more than eight years of fighting, the Soviet Army begins to withdrawal 115,000 troops from Afghanistan. |
| 55572 | May.15 | Event | 1991 – Édith Cresson becomes France's first female premier. |
| 55573 | May.15 | Event | 1997 – The United States government acknowledges the existence of the "Secret War" in Laos and dedicates the Laos Memorial in honor of Hmong and other "Secret War" veterans. |
| 55574 | May.15 | Event | 2006 – Cloud Gate was formally dedicated in Chicago's Millennium Park. |
| 55575 | May.15 | Event | 2008 – California becomes the second U.S. state after Massachusetts in 2004 to legalize same-sex marriage after the state's own Supreme Court rules a previous ban unconstitutional. |
| 55576 | May.15 | Event | 2010 – Jessica Watson becomes the youngest person to sail, non-stop and unassisted around the world solo. |
| 55577 | May.15 | Event | 2013 – An upsurge in violence in Iraq leaves more than 389 people dead over three days. |
| 55578 | May.15 | Birth | 1397 – Sejong the Great, Korean king (d. 1450) |
| 55579 | May.15 | Birth | 1531 – Maria of Austria, Duchess of Jülich-Cleves-Berg (d. 1581) |
| 55580 | May.15 | Birth | 1567 – Claudio Monteverdi, Italian priest and composer (d. 1643) |
| 55581 | May.15 | Birth | 1608 – René Goupil, French-American missionary and saint (d. 1642) |
| 55582 | May.15 | Birth | 1689 – Lady Mary Wortley Montagu, English author and playwright (d. 1762) |
| 55583 | May.15 | Birth | 1720 – Maximilian Hell, Hungarian priest and astronomer (d. 1792) |
| 55584 | May.15 | Birth | 1749 – Levi Lincoln, Sr., American lawyer and politician, 4th United States Attorney General (d. 1820) |
| 55585 | May.15 | Birth | 1759 – Maria Theresia von Paradis, Austrian pianist and composer (d. 1824) |
| 55586 | May.15 | Birth | 1764 – Johann Nepomuk Kalcher, German organist and composer (d. 1827) |
| 55587 | May.15 | Birth | 1767 – Ezekiel Hart, Canadian businessman and politician (d. 1843) |
| 55588 | May.15 | Birth | 1773 – Klemens von Metternich, German-Austrian politician, 1st State Chancellor of the Austrian Empire (d. 1859) |
| 55589 | May.15 | Birth | 1786 – Dimitris Plapoutas, Greek general and politician (d. 1864) |
| 55590 | May.15 | Birth | 1808 – Michael William Balfe, Irish composer and conductor (d. 1870) |