The following is a timeline of the history of Brussels, Belgium, in the 20th century.
1901–1913 – La Belle Époque 1901 – The Maison & Atelier Horta is built.
1902 À la Mort Subite café is built. The is built. The Sino-Belgian Bank is established at the request of King Leopold II. The Sonian Forest Railway begins operation, connecting Petite-Espinette/Kleine Hut to Boitsfort/Bosvoorde railway station. The Brussels Motor Show is first held. Jean Neuhaus invents the praline. 12 April: in the Marolles/Marollen during the Belgian general strike of 1902. 15 November: An of King Leopold II by Gennaro Rubino takes place. 16 November: The Solvay Institute of Sociology is established by industrialist Ernest Solvay. 1903 café is built. The École de Commerce Solvay business school is founded with a donation from Ernest Solvay. December: The socialist starts publication. 1904 The Saint-Gilles Municipal Hall is built. 26 June: Josaphat Park opens.
1905 The Cauchie House is built. Buses begin operating in the city. 21 September: St. Michael's College opens in Etterbeek. 25 September: The Cinquantenaire Arcade is completed. 1906 Buffalo Bill's Wild West Show takes place. 13 January: Besix is founded by the Stulemeijer family. 7 February: The dismembered body of Jeanne Van Calck is found at 22, /. 24 February: Chilean diplomat Ernesto Balmaceda Bello is shot dead by Carlos Waddington, the brother of his fiancé Adelaida Waddington. 2 May: The is established. 1907 – 1 December: Annette Bellot is abducted while playing near the Place de Brouckère/De Brouckèreplein, and is found the next day raped and strangled near the Royal Veterinary School of Cureghem. 1908 The Chapel of the Resurrection is built. The is established in . Verregat Hippodrome is established. 27 May: R.S.C. Anderlecht is founded. 1909 6 December: Adolphe Max is appointed mayor by royal decree. 23 December: King Albert I takes the constitutional oath at the Palace of the Nation.
1910 The Hotel Astoria opens on the Rue Royale/Koningsstraat. The original Mont des Arts/Kunstberg is inaugurated. Henri Wittamer opens a bakery with his wife on the Square du Grand Sablon/Grote Zavelsquare. 10 March: Le Mariage de mademoiselle Beulemans is first performed at the Théâtre de l'Olympia. 23 April–1 November: The Brussels International world's fair is held. 14–15 August: A fire destroys part of the section of the Brussels International Exposition. 23 September: The Brussels Convention on Assistance and Salvage at Sea is signed.
1911 The Stoclet Palace is built. The North–South connection begins construction. 16–17 April: The Schaerbeek Municipal Hall is partially destroyed by a suspected arson fire. 30 October–3 November: The first Solvay Conference is held. 23 December: The Cercle de la Toison d'Or private club is founded. 1912 The Young Trade Unionists is established by Joseph Cardijn. At the request of Charles Pathé, the French director Alfred Machin establishes Belgium's first film studio at Karreveld Castle. 14 October: Polish Dominican priest, count, academic and mystic Joachim Badeni is born in the city. 1913 The Belle-Vue Brewery is established. 14–24 April: The Belgian general strike of 1913 takes place. 5 October: The opens on the edge of Josaphat Park.
1914–1918 – First World War 1914 27 March: Albert Hustin becomes the first person to successfully perform non-direct blood transfusions using sodium citrate as an anticoagulant at the St. John's Clinic. 1 May: Tram line 81 begins service. 11 May–4 June: The is held. 21 August: World War I: The city is captured and occupied by the German Army. 26 August: The city becomes the seat of the Imperial German General Government of Belgium. The Imperial German Air Service establishes Flugplatz Brüssel military airfield in Haren. 29 November: The pro-German starts publication.
1915 7 June: A Zeppelin hangar on Flugplatz Brüssel is partially destroyed during an attack on airship LZ38. October: René Magritte moves from Charleroi to the city to study at the Royal Academy of Fine Arts. 12 October: Edith Cavell is executed by firing squad at the Tir National/Nationale Schietbaan. 1916 – 1 April: Gabrielle Petit is executed by firing squad at the Tir National. 1917 The Emile Versé Stadium opens. 4 February: The Council of Flanders is established by the "activist" faction of the Flemish Movement, with covert backing from Germany. 1918 10 November: The Brussels Soldiers' Council is established by German troops in German-occupied Belgium. 17 November: Adolphe Max returns triumphantly to loud cheers from the city's residents after his time in Germany. 22 November: King Albert I returns to the city.
1919–1939 – Interwar period 1919 Population: 685,268 metro. The Lignes Farman airline begins operating its Paris–Brussels route. The New University is reintegrated into the Free University. 15 October: Schaerbeek Municipal School No. 15 opens in Uitkerke to provide schooling for children with health problems. 1920 The Oscar Bossaert Stadium opens. The Mundaneum opens. 6 July: The University Foundation is established by Herbert Hoover, Emile Francqui and Léon Delacroix. 15–26 August: The fencing events of the 1920 Summer Olympics are held at the Egmont Palace. 20 August: Belga news agency is established by Pierre-Marie Olivier and Maurice Travailleur in Schaerbeek. 28 August–5 September: Some of the football events of the Summer Olympics are held in the Joseph Marien Stadium. 25 September–8 October: The International Financial Conference is held in the city. 1921 – 30 March: Haren, Laeken and Neder-Over-Heembeek are annexed by the City of Brussels. 1922 The is established. The is established. 22 September: Jan Baptist De Mey is reported missing and over the following weeks his dismembered remains are accidentally discovered in the Brussels Canal. 12 November: Tour & Taxis officially opens. 1923 The Royal Museum of the Armed Forces and Military History opens. opens. Het Heideken social garden city begins development. 1 January: The is established. 2 January: Tram line 23 begins service. 23 May: The (Sabena) is established. 1924 – Verregat social garden city begins development.
1925 – St Andrew's Church is consecrated. 1926 The École nationale supérieure des arts visuels de La Cambre (ENSAV) is established. The Comme chez Soi restaurant is established. 1927 – 24–29 October: The fifth Solvay Conference, perhaps the most famous, is held. 1928 The Charlier Museum opens. The Villa van Buuren is built. The first Fernand Jacobs Award is presented to Louis Crooy and Victor Groenen in honour of Fernand Jacobs. 1929 4 January: Tintin first appears in Le Petit Vingtième newspaper. 19 October: The Centre for Fine Arts opens. 1930 Population: 200,433 city. The Hotel Le Plaza opens. The Church of Our Lady of Victories at the Sablon becomes the Belgian lieutenancy of the Equestrian Order of the Holy Sepulchre of Jerusalem. The fashion house is established. 18 June: The (NIR) is established. 23 August: The Jubilee Stadium opens. 6 December: Casal Català de Brussel·les is founded by a group of Catalan exiled politicians including Francesc Macià i Llussà and Bonaventura Gassol i Rovira. 1931 The Brussels Symphony Orchestra is founded. The Granvelle Palace is demolished. 1932 – 7 October: The Luna-Theater opens on the site of a former luna park. 1933 The Uccle Crematorium opens, becoming the first crematorium in Belgium. 6 April: The Synagogue of Anderlecht is consecrated. 8 March: The is established. 1934 The Villa Empain is built. The Citroën Garage is built. 22 February: The funeral of King Albert I takes place. 23 February: King Leopold III takes the constitutional oath at the Palace of the Nation.
1935 The Brussels International world's fair is held; the Palais des Expositions is built. The Basilica of the Sacred Heart is consecrated. The Groot Symfonie-Orkest is established. The Société royale de Flore de Bruxelles and merge and form the . 1937 King Leopold III commissions the world's first six-metre-high concrete climbing wall, built in the garden of the Château of Stuyvenberg. The Résidence de la Cambre, the city's first high-rise, is constructed. 21 March–1 April: The first Eugène Ysaÿe Competition is held. 1938 The Forest Municipal Hall is built. The Flagey Building is built. is established. 28 February: Bossemans et Coppenolle is first performed at the . 9 April: The Royal Belgian Film Archive is established by André Thirifays, Henri Storck and Piet Vermeylen. 1939 The Constantin Meunier Museum opens. 21 June: The Institut Jules Bordet is inaugurated. September: Construction of the K-W Line begins to defend the city from invasions. 28 November: Joseph Van De Meulebroeck is appointed mayor by royal decree.
1940–1945 – Second World War
1940 10 May: The Third Reich launches a surprise attack, air raid sirens ring in the city, and bombs hit Woluwe-Saint-Pierre, Etterbeek, Evere, and Schaerbeek. 11 May: Bombs are dropped in the vicinity of the North and South stations and Schaerbeek. 12 May: The city is mostly deserted, with only a few trams running, schools closed, and many residents fleeing south and west. 16 May: British troops move east across the city and return when the bridges over the Willebroek and Brussels-Charleroi canals are blown up. 17 May: The German occupation begins as the city is declared open, and the Sixth Army, under General Walter von Reichenau, enters, while the flees to Bordeaux. 28 May: The Belgian Army surrenders, and King Leopold III is taken prisoner of war at the Palace of Laeken. 31 May: The German Military Administration in Belgium and Northern France is headquartered in the city. 1 June: Adolf Hitler visits the city. 1 July: The intelligence network in formed by employees of the Bank of Brussels. 20 July: The Frontstalag 110 prisoner-of-war camp is established by the Wehrmacht. 31 July: The and radio stations are established by the Military Administration. 15 August: La Libre Belgique clandestine newspaper begins its publication. 18–19 August: English bombs hit the , killing seven. 11 November: A demonstration at the Tomb of the Unknown Soldier is broken up. 17 December: The Belgian National Movement is established. 1941 1 February: and clandestine newspapers begin their publication by the Communist Party of Belgium. 13 March: The Frontstalag 110 POW camp is dissolved. 29 May: The 'Hunger march for the release of prisoners of war', 3,000 women rally behind slogans and march through the city. June: A passenger train derails in Uccle after a failed sabotage attempt by the Belgian National Movement of a tank transport from Charleroi on . 30 June: Joseph Van De Meulebroeck is arrested and deported; is designated deputy mayor. 18 August: The Comet Line starts operating. 10 October: Bombing of the Rex headquarters on the ; Jean-Joseph Oedekerken is killed. 25 November: The Free University of Brussels closes. 1942 January: Groupe G is formed by a group of former students of the Free University. 10 March: Violence erupts in the city during a parade of the Walloon Legion before leaving for the Eastern Front, marked by bombings and attacks from communist militants against collaborators and military targets. 3 September: A razzia occurs in the Marolles, 718 are arrested and transported to Dossin. 24 September: is formed by merging 18 municipalities into the City of Brussels; Jan Grauls is appointed mayor. 1943 2 January: Following several attacks on Germans, sanctions are imposed as theatres and concert halls close, sports matches are cancelled and night trams stop running. 20 January: An attack on the Gestapo headquarters by Baron Jean de Selys Longchamps takes place. 29 January: The sanctions imposed earlier that month are lifted. 14 April: Paul Colin is assassinated by Arnaud Fraiteur.