1928 1929 1930 - 1931 - 1932 1933 1934
1900s 1910s 1920s - 1930s - 1940s 1950s 1960s
Events of 1931
- January 2 – South Dakota native Ernest Lawrence invents the cyclotron, used to accelerate particles to study nuclear physics.
- January 4 – German pilot Elly Beinhorn begins her flight to Africa.
- January 6 – Thomas Edison submits his last patent application.
- January 22 – Sir Isaac Isaacs is sworn in as the first Australian-born Governor-General of Australia.
- January 25 – Mohandas Gandhi is released again in India.
- January 27 – Pierre Laval forms a government in France.
- February 3 – Hawke's Bay earthquake: Much of the New Zealand city of Napier is destroyed in an earthquake measuring 7.9 on the Richter scale.
- February 10 – New Delhi becomes the capital of India.
- February 12 – Radio Vaticana first broadcasts.
- February 16 – Pehr Evind Svinhufvud is elected president of Finland.
- February 20 – California gets the go-ahead by the U.S. Congress to build the San Francisco – Oakland Bay Bridge.
- February 21 – Peruvian revolutionaries hijack a Ford Trimotor aeroplane and demand that the pilot drop propaganda leaflets over Lima.
- March 1 – The USS Arizona is placed back in full commission after a refit.
- March 3 – The Star-Spangled Banner is adopted as the United States National anthem.
- March 4 – The British viceroy of India and Mohandas Gandhi negotiate.
- March 7 – The new House of Representatives opens in Helsinki, Finland.
- March 11 – The Ready for Labour and Defence of the USSR programme, abbreviated as GTO, is introduced in the Soviet Union.
- March 17 – Nevada legalizes gambling.
- March 23 – Indian revolutionary leaders Bhagat Singh, Rajguru and Sukhdev are hanged by the British Government.
- March 25 – The Scottsboro Boys are arrested in Alabama and charged with rape.
- March 31 – An earthquake destroys Managua, Nicaragua, killing 2,000 people.
- April 6 – The Portuguese government declares martial law in Madeira and in the Azores because of an attempted military takeover in Funchal.
- April 9 – Argentinian anarchist Severino Digiovanni is executed.
- April 14 – The Second Spanish Republic is proclaimed in Madrid.
- April 15 – The Castellemmarese War ends with the assassination of Joe "The Boss" Masseria, briefly leaving Salvatore Maranzano as capo di tutti i capi ("boss of all bosses") and undisputed ruler of the American Mafia. Maranzano is himself assassinated less than 6 months later, leading to the establishment of the Five Families.
- April 22 – Austria, Britain, Denmark, Germany, Italy, Sweden and the USA recognize the Spanish Republic.
- May 1 – Construction of the Empire State Building is completed in New York City.
- May 4 – Kemal Atatürk is re-elected president of Turkey.
- May 11 The Creditanstalt, Austria's largest bank, goes bankrupt, beginning the banking collapse in Central Europe that causes a worldwide financial meltdown.
- May 13 – Paul Doumer is elected president of France.
- June 5 – German Chancellor Dr. Heinrich Brüning visits London, where he warns the British Prime Minister Ramsay MacDonald that the collapse of the Austrian banking system, caused by the bankruptcy of the Creditanstalt, has left the entire German banking system on the verge of collapse.
- June 14 – The overloaded pleasure craft Saint-Philibert, carrying trippers home to Nantes from Île de Noirmoutier, sinks at the mouth of the river Loire in France; over 450 drown.
- June 19 -In an attempt to stop the banking crisis in Central Europe from causing a worldwide financial meltdown, President Herbert Hoover issues the Hoover Moratorium.
- June 23 – Wiley Post and Harold Gatty take off from Roosevelt Field, Long Island in an attempt to accomplish the first round-the-world flight in a single-engine plane. 
- July – John Haven Emerson of Cambridge, Massachusetts perfects the Emerson iron lung just in time for the growing polio epidemic.
- July 1 – Milan Central Station officially opens in Italy.
- July 16 – Emperor Haile Selassie signs the first constitution of Ethiopia.
- The Huang He floods kill between 850,000 and 4,000,000 people (the deadliest historic natural disaster).
- July 26 – The millennialist Bible Student movement adopts the name Jehovah's Witnesses at a meeting in Columbus, Ohio.
- August 24 – The Labour Government of Ramsay MacDonald resigns in Britain, replaced by a National Government of people drawn from all parties, also under MacDonald.
- August 31 – The Yangtze River floods, leaving 23 million homeless.
- September 10 – The worst hurricane in Belize history kills an estimated 1,500 people.
- September 15 – Invergordon Mutiny: Strikes are called in the Royal Navy due to decreased salaries.
- September 16 – Hanging of Omar Mukhtar.
- September 18 – Japan stages the Mukden Incident as a pretext to occupy Manchuria.
- October 17 – American gangster Al Capone is sentenced to 11 years in prison for tax evasion in Chicago, Illinois.
- October 24 – The George Washington Bridge is dedicated; it opens to traffic the following day.
- November 6 – Indian spiritual leader Meher Baba arrives in America for the first time.
- November 7 – The Chinese Soviet Republic is proclaimed by Mao Zedong.
- November 8
- December 8 – Carl Friedrich Goerdeler is appointed Reich Price Commissioner in Germany to enforce the deflationary policies of the Brüning government.
- December 10 – Niceto Alcalá-Zamora is elected president of the Spanish Republic.
- December 11 – The British Parliament enacts the Statute of Westminster, which establishes a status of legislative equality between the self-governing dominions of the Commonwealth of Australia, the Dominion of Canada, the Irish Free State, Newfoundland, the Dominion of New Zealand, and the Union of South Africa.
- December 13 – Wakatsuki Reijiro resigns as Prime Minister of Japan.