This is a list of selected March 31 anniversaries that appear in the "On this day" section of the Main Page. To suggest a new item, in most cases, you can be bold and edit this page. Before doing so, please review the selected anniversaries guidelines. If your suggestion is potentially controversial or relates to a day currently or soon to appear on the Main Page, post it on the talk page instead.
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- Only four or five events are featured each day; therefore, not all important or significant events can be included.
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March 31: César Chávez Day in various U.S. states; Freedom Day in Malta
- 1854 – U.S. Navy Commodore Matthew C. Perry and the Tokugawa shogunate signed the Convention of Kanagawa, forcing the opening of Japanese ports to American trade.
- 1889 – The Eiffel Tower (pictured) was inaugurated in Paris, becoming a global icon of France and one of the most recognizable structures in the world.
- 1917 – The Danish West Indies became the U.S. Virgin Islands after the United States paid Denmark US$25 million for the Caribbean islands.
- 1930 – To avoid government censorship, Hollywood movie studios instituted their own set of industry censorship guidelines, popularly known as the Hays Code.
- 1951 – The first UNIVAC I, the first commercial computer made in the United States, was delivered to the United States Census Bureau.
- 1995 – Mexican American singer Selena, known as "The Queen of Tejano music", was shot and killed in Corpus Christi, Texas, by the president of her fan club, Yolanda Saldívar.