| 30 September 1061 | Holy Roman Empire, Italy [administration] | Following the death of Pope Nicholas II (22 July), Anselm of Baggio, bishop of Lucca is elected as Pope Alexander II, the first pope elected according to the election decree of Nicholas II. |
| 30 September 1626 | China, Ming Empire, Manchuria [political events] | Following the death of Nurhachi, the emperor who united the Manchu and Juchen peoples under his own authority, his son Abahai succeeds him as khan. |
| 30 September 1688 | UK, United Netherlands [diplomacy] | The Dutch stadtholder William of Orange accepts the Whig lords' invitation to intervene in British affairs. He issues a manifesto denouncing evil counsellors, who he claimed had subjected the country to arbitrary government, and calling for a free Parliament. |
| 30 September 1846 | USA [dentistry] | US dentist William Thomas Morton gives the first successful demonstration of ether as an anaesthetic during a dental operation to extract a tooth. He uses it in Boston, Massachusetts, on 16 October, to anaesthetize a patient while removing a tumour from his neck. |
| 30 September 1868 | Spain [revolution] | Queen Isabella II of Spain flees to France and is declared deposed, following the Liberal revolt against her rule. |
| 30 September 1882 | USA [energy] | The world's first hydroelectric generating plant opens at Appleton, Wisconsin. It consists of two direct current generators powered by a 107 cm/42 in waterwheel. It produces 2.5 kW of power. |
| 30 September 1882 | Germany [births and deaths] | Hans Geiger, German physicist who invents the Geiger counter to measure radioactivity, born in Neustadt-an-der-Haardt, Germany (–1945). |
| 30 September 1918 | Bulgaria [treaties] | Bulgaria signs an armistice with the Allies. |
| 30 September 1924 | [births and deaths] | Truman Capote, US playwright and novelist, born in New Orleans, Louisiana (–1984). |
| 30 September 1927 | USA [baseball] | The US baseball player Babe Ruth of the New York Yankees sets a major league record of 60 home runs in a season. The record stands until 1961 when Roger Maris, also of the Yankees, hits 61, from 7 more games. |
| 30 September 1929 | [aircraft] | German car manufacturer Fritz von Opel test-pilots the first rocket-powered aircraft, a glider with a gunpowder rocket attached. |
| 30 September 1938 | Germany, Czechoslovakia, UK, France, Italy [diplomacy] | The Munich Agreement is signed in Munich, Germany, by the British prime minister, the French prime minister, the German Führer, and the Italian prime minister. It permits Germany to annex the Sudetenland in western Czechoslovakia. Chamberlain returns to London, England, speaking of ‘peace with honour’ and ‘peace in our time’. |
| 30 September 1961 | world [international organizations] | The Organization for Economic Cooperation and Development (OECD), established the previous year by an international convention. is founded. It is a successor to the Organization for European Economic Cooperation (OEEC), but the OECD includes the USA and Canada among its founder members. |
| 30 September 1967 | UK [radio] | The British Broadcasting Corporation (BBC) launches a national pop music station, Radio 1. The first programme is The Breakfast Show, presented by Tony Blackburn, and the first record played is ‘Flowers in the Rain’ by the Move. |
| 30 September 1978 | Tuvalu, UK [decolonization] | Tuvalu, formerly the Ellice Islands, in the southwest Pacific, gains its independence from Britain. |
| 30 September 1982 | USA [television] | Cheers, a popular situation comedy about several characters who hang out in a bar in Boston, is shown on US television. |
