- New Year's Day was celebrated on January 1 for the first time. (45 BC) The Julian calendar, created by Julius Caesar, came into effect on this day. Before Caesar's calendar, most of the world followed a lunar calendar, which often put the dates out of sequence with the seasons. Though celebrating New Year's on the first fell out of fashion in the Middle Ages, it came back in style with the introduction of the Gregorian calendar in 1582, and has been celebrated that way ever since.
- Y2K occurred — and nothing happened. (2000) Many people thought that the changing of the millennium would cause a collapse of all computerized systems, including banks and businesses. Others claimed that the changing of the millennium would be the end of the world. With a few minor exceptions, none of the anticipated crises occurred.
- The Emancipation Proclamation came into effect. (1863) The act freed more than three million slaves, but contrary to popular belief, it did not free all slaves. The Emancipation Proclamation only applied to slaves in the Deep South, and many people remained enslaved until after the end of the Civil War in 1865.
- Cigarette advertisements were shown for the last time on US television. (1971) Congress has passed a Public Health Smoking Act the year before that came into effect on January 2, 1971. The last cigarette advertisement shown on TV was for Virginia Slims.
- The first traveler's check was issued. (1772) The London Credit Exchange Company offered traveler's checks that could be used in 90 European cities.
- AT&T lost 22 of its companies as part of an anti-trust settlement. (1984) The company had been found to be in violation of anti-trust laws, and had to give up two-thirds of its employees and almost $100 billion US Dollars (USD) in assets.
- The Euro became the official currency of 11 countries (1999) All the members of NATO began using it, with the exception of the United Kingdom, Denmark, Greece, and Sweden.
- The Commonwealth of Australia came into being. (1901) Australia had existed as five separate British colonies before, but came into its modern form of government on this day.
- Fidel Castro ousted the Cuban dictator Batista. (1959) Castro had been trying to topple Batista since the early 1950s. He finally succeeded, and Batista fled the island on this day. Thousands of Cubans celebrated in the streets when he left, and Castro came into Havana the following week.
- While while incarcerated in San Quentin prison, Merle Haggard heard Johnny Cash sing. (1958) Haggard had been in and out of prisons since childhood, and seeing Cash perform was what made him decide to become a singer. Haggard went on to become a famous country musician.