| 1799–1825 | [maths] | The French mathematician and physicist Pierre-Simon Laplace publishes the five-volume Traité de mécanique céleste/Celestial Mechanics, which applies calculus to the motions of celestial bodies and Isaac Newton's theories of the Solar System to show how its stability is implicit in the law of gravitation. |
| 1800–1850 | USA [consumer products] | A revolution in retail and wholesale trade occurs: specialization transforms the urban retail market, replacing the general store with individual stores for hardware, groceries, dry goods, furnishing, books, tobacco, and so on. Cash-only sales policies are instituted around 1806. |
| 1809 | France [biology] | French biologist Jean-Baptiste de Lamarck publishes Philosophie zoologique/Zoological Philosophy in which he theorizes that organs improve with use and degenerate with disuse and that these environmentally adapted traits are inheritable. He also proposes a progressive theory of evolution. |
| 1809 | Germany [fiction] | The German writer Johann Wolfgang von Goethe publishes his novel Wahlverwandtschaften/The Elective Affinities. |
| 19 January 1809 | USA [births and deaths] | Edgar Allan Poe, US poet, critic and short-story writer, born in Boston, Massachusetts (–1849). |
| 12 February 1809 | USA [births and deaths] | Abraham Lincoln, sixteenth president of the USA 1861–65, a Republican, born in Hodgenville, Kentucky (–1865). |
| 12 February 1809 | England [births and deaths] | Charles Robert Darwin, English naturalist who develops the theory of evolution through natural selection, born in Shrewsbury, Shropshire, England (–1882). |
| 29 March 1809 | Sweden [wars] | King Gustavus IV Adolphus of Sweden is forced to abdicate after military defeats in war with Denmark. |
| 12 May 1809 | UK, France, Portugal [Napoleonic Wars (1803–15)] | British forces under Arthur Wellesley (later Duke of Wellington) defeat the French under Marshal Nicolas-Jean Soult at Oporto and force them to retreat from Portugal. |
| 17 May 1809 | Papal States, France [political events] | The French emperor Napoleon I issues an imperial decree annexing the Papal States, following their occupation by France in February 1808. |
| 31 May 1809 | Austria [births and deaths] | Franz Josef Haydn, Austrian classical composer, dies in Vienna, Austria (77). |
| 8 June 1809 | USA, UK [births and deaths] | Thomas Paine, British-born American political pamphleteer whose writings influenced the American Revolution, dies in Boston, Massachusetts (72). |
| 5 July - 6 July 1809 | France, Austrian Empire [Napoleonic Wars (1803–15)] | The French emperor Napoleon I defeats the Austrian army under Archduke Charles in the Battle of Wagram, near Vienna, although the Austrian army retreats in good order. |
| 28 July 1809 | UK, France, Spain [Napoleonic Wars (1803–15)] | The British soldier and statesman Arthur Wellesley is victorious at the Battle of Talavera in Spain over the French who afterwards fall back to Madrid. Wellesley is subsequently created Duke of Wellington. |
| 29 December 1809 | England [births and deaths] | William Ewart Gladstone, prime minister of Britain 1868–74, 1880–85, 1886, and 1892–94, a Liberal, born in Liverpool, England (–1898). |
