| 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. |
| 1810–1859 | USA [agriculture] | US cotton production, the vast majority of which is grown in the southern states, rises from 171,000 bales in 1810 to just under 5.4 million in 1859. |
| 1831–1840 | USA, UK [statistics and demography] | Emigration to the USA is 75,810 from Britain and 207,381 from Ireland. |
| 1840 | UK [science] | English philosopher William Whewell publishes The Philosophy of Inductive Sciences, Founded upon Their History, in which he describes how the sciences use induction to arrive at general propositions. |
| 1840 | UK [science] | English microscopist John Dancer takes the first photographs of microscopic objects; they are magnified up to twenty times. |
| 1840 | France [social theory] | The French socialist Pierre-Joseph Proudhon publishes Qu'est-ce-que La Propriété?/What is Property? It contains the famous proposition: ‘Property is theft.’ |
| 1840 | Germany [songs] | The German composer Robert Schumann completes his Liederkreis/Song Cycle (Opus 39), settings of poems by the German poet Joseph, Baron von Eichendorff; and Frauenliebe und Leben/Woman's Love and Life (Opus 42). He also completes his Liederkreis/Song Cycle (Opus 24) and Dichterliebe/Poet's Love (Opus 48), both settings of poems by the German poet Heinrich Heine. |
| 1840 | UK [photography] | English scientist William Fox Talbot improves his earlier photographic process. Paper is treated with silver nitrate, potassium iodide, and gallic acid. After exposure the image is fixed with a solution of potassium bromide, later replaced by sodium hyposulphite. |
| 1840–1860 | world [plagues and epidemics] | A cholera pandemic kills millions of people worldwide. |
| 1840 | world [plagues and epidemics] | A second worldwide cholera epidemic begins. |
| 1840–1850 | USA [farming] | Wheat becomes an increasingly important cash crop in the USA; production in 1839 is nearly 85 million bushels and climbs to over 100 million bushels in 10 years. |
| 1840 | Russia [fiction] | The Russian writer Mikhail Yuryevich Lermontov publishes his novel Geroy nashego vremeni/A Hero of Our Time. |
| 1840 | England [fiction] | The English writer Charles Dickens begins publishing his novel The Old Curiosity Shop in serial form. It appears as a book in 1841. |
| 1840 | USA [industrialization] | Cotton textiles become the leading US industry, with 1,778,000 spindles and 75,000 workers. |
| 10 January 1840 | UK [postal services] | The British Post Office official Rowland Hill introduces the penny post in Britain, with an agreed standard rate for postal deliveries which replaces fees based on the distance and difficulty of the route. |
| 5 February 1840 | New Zealand, UK [treaties] | By the Treaty of Waitangi, New Zealand Maori chiefs surrender their sovereignty to the British government. |
| 2 April 1840 | France [births and deaths] | Emile Zola, French novelist and critic who founds the Naturalist movement, born in Paris, France (–1902). |
| 1 May 1840 | UK [everyday life] | The world's first postage stamp, the Penny Black, is issued in Britain, the first adhesive stamp to be used commercially. |
| 7 May 1840 | Russia [births and deaths] | Peter Illich Tchaikovsky, leading 19th-century Russian composer who, amongst a great variety of works, composes the music for the ballets Swan Lake, The Nutcracker, and Sleeping Beauty, born in Votkinsk, Russia (–1893). |
| 2 June 1840 | England [births and deaths] | Thomas Hardy, English novelist and poet, born in Bockhampton, Dorset, England (–1928). |
| 15 July 1840 | Russian Empire, UK, Prussia, Austrian Empire, Egypt, Ottoman Empire, Crete [treaties] | Russia, Britain, Prussia, and Austria form the Quadruple Alliance in support of the Ottoman Empire and by the Treaty of London offer Egypt to its ruler and Ottoman opponent, Mehmet Ali, as a hereditary possession and also southern Syria for life, provided he gives up Crete and northern Syria. He refuses, in the hope of French aid. |
| 5 November 1840 | Egypt, Ottoman Empire [treaties] | By the Convention of Alexandria the Egyptian viceroy Mehmet Ali agrees to the terms of the Treaty of London of 15 July, ending the Ottoman-Egyptian war. |
| 5 November 1840 | Afghanistan, UK [wars] | The First Anglo-Afghan War ends when Afghan forces surrender to the British in Afghanistan. |
| 12 November 1840 | France [births and deaths] | Auguste Rodin, French sculptor reknowned for his realistic treatment of the human figure, born in Paris, France (–1917). |
| 14 November 1840 | France [births and deaths] | Claude Monet, French Impressionist painter, born in Paris, France (–1926). |
| 2 December 1840 | USA [elections] | Americans elect William Henry Harrison president and John Tyler vice president. |
