| 143071 | December 20 | Event | 1971 – The international aid organization Doctors Without Borders is founded by Bernard Kouchner and a group of journalists in Paris, France. |
| 143072 | December 20 | Event | 1973 – The Prime Minister of Spain, Admiral Luis Carrero Blanco, is assassinated by a car bomb attack in Madrid. |
| 143073 | December 20 | Event | 1977 – Djibouti and Vietnam join the United Nations. |
| 143074 | December 20 | Event | 1984 – The Summit Tunnel fire is the largest underground fire in history, as a freight train carrying over 1 million liters of gasoline derails near the town of Todmorden, England, in the Pennines. |
| 143075 | December 20 | Event | 1985 – Pope John Paul II announces the institution of World Youth Day. |
| 143076 | December 20 | Event | 1987 – In the worst peacetime sea disaster, the passenger ferry Doña Paz sinks after colliding with the oil tanker Vector in the Tablas Strait in the Philippines, killing an estimated 4,000 people (1,749 official). |
| 143077 | December 20 | Event | 1988 – The United Nations Convention Against Illicit Traffic in Narcotic Drugs and Psychotropic Substances is signed in Vienna, Austria. |
| 143078 | December 20 | Event | 1989 – United States invasion of Panama: The United States sends troops into Panama to overthrow government of Manuel Noriega. This is also the first combat use of purpose-designed stealth aircraft. |
| 143079 | December 20 | Event | 1991 – A Missouri court sentences the Palestinian militant Zein Isa and his wife Maria to death for the honor killing of their daughter Palestina. |
| 143080 | December 20 | Event | 1995 – NATO begins peacekeeping in Bosnia. |
| 143081 | December 20 | Event | 1995 – American Airlines Flight 965, a Boeing 757, crashes into a mountain 50 km north of Cali, Colombia killing 159. |
| 143082 | December 20 | Event | 1996 – NeXT merges with Apple Computer, starting the path to Mac OS X. |
| 143083 | December 20 | Event | 1999 – Macau is handed over to China by Portugal. |
| 143084 | December 20 | Event | 2004 – A gang of thieves steal £26.5 million worth of currency from the Donegall Square West headquarters of Northern Bank in Belfast, Northern Ireland, United Kingdom, one of the largest bank robberies in British history. |
| 143085 | December 20 | Event | 2005 – Aleksandër Moisiu University was founded in Durrës, Albania. |
| 143086 | December 20 | Event | 2007 – Elizabeth II becomes the oldest monarch of the United Kingdom, surpassing Queen Victoria, who lived for 81 years, 7 months and 29 days. |
| 143087 | December 20 | Event | 2007 – The Portrait of Suzanne Bloch (1904), by the Spanish artist Pablo Picasso, and O Lavrador de Café by Brazilian modernist painter Cândido Portinari, are stolen from the São Paulo Museum of Art. |
| 143088 | December 20 | Event | 2013 – China successfully launches the Bolivian Túpac Katari 1 from the Xichang Satellite Launch Center. |
| 143089 | December 20 | Event | 2014 – Two police officers of the New York City Police Department are shot and killed, allegedly in retaliation against the deaths of Eric Garner and Michael Brown. |
| 143090 | December 20 | Birth | 1494 – Oronce Finé, French mathematician and cartographer (d. 1555) |
| 143091 | December 20 | Birth | 1537 – John III of Sweden (d. 1592) |
| 143092 | December 20 | Birth | 1626 – Veit Ludwig von Seckendorff, German scholar and politician (d. 1692) |
| 143093 | December 20 | Birth | 1641 – Urban Hjärne, Swedish chemist, geologist, and physician (d. 1724) |
| 143094 | December 20 | Birth | 1717 – Charles Gravier, comte de Vergennes, French politician and diplomat, French Minister of Foreign Affairs (d. 1787) |
| 143095 | December 20 | Birth | 1740 – Arthur Lee, American physician and diplomat (d. 1792) |
| 143096 | December 20 | Birth | 1786 – Pietro Raimondi, Italian composer (d. 1853) |
| 143097 | December 20 | Birth | 1792 – Nicolas Toussaint Charlet, French painter (d. 1845) |
| 143098 | December 20 | Birth | 1833 – Samuel Mudd, American physician (d. 1883) |
| 143099 | December 20 | Birth | 1838 – Edwin Abbott Abbott, English theologian, author, and educator (d. 1926) |
| 143100 | December 20 | Birth | 1841 – Ferdinand Buisson, French academic and politician, Nobel Prize laureate (d. 1932) |