The “Exposition Universelle et Internationale de Bruxelles - Wereldtentoonstelling Brussel 1958,” popularly known as Expo 58, was held on the Heysel plateau in Brussels, Belgium, from April 17 to October 19, 1958. Registered by the International Exhibitions Bureau (Bureau International des Expositions, BIE) as a general exhibition of the first category, it was organized by the Executive Committee of the Society of the Exhibition. It is commonly described as the first Expo after World War II, but that is accurate only for its category: it was the first general exhibition of the first category held after the war. The BIE lists 12 Expos between the end of the war and its opening: Expo 1947 Paris, Expo 1949 Stockholm, Expo 1949 Lyon, Expo 1949 Port-au-Prince (a general exhibition of the second category), Expo 1951 Lille, Expo 1953 Jerusalem, Expo 1953 Rome, Expo 1954 Naples, Expo 1955 Turin, Expo 1955 Helsingborg, Expo 1956 Beit Dagon and Expo 1957 Berlin. King Baudouin opened the Expo on April 17, 1958, and over its six months it recorded 41,454,412 visits.

Brussels brought long experience to the project. The city had hosted international exhibitions in 1888, 1897, 1910 and 1935, and Expo 58 would make it a host for the fifth time. The Atomium's history of the event notes that Belgium's record as a host weighed in its favor when Brussels was chosen over proposals associated with Paris and London. The BIE registered the Expo at its 32nd General Assembly on November 5, 1953, giving the organizers four and a half years to prepare.

The theme, "A World View: A New Humanism," presented science and technology as tools for human progress, while insisting that moral development keep pace with them. In his opening speech, King Baudouin made that point directly, arguing that technology alone does not make a civilization. Nuclear energy was a central subject: a display promoted the peaceful atom under the motto "Atom = Hope" and included a scale model of the BR-3 reactor at Mol.

The BIE counts 39 participating countries, while the Atomium's history describes an Expo of Belgium and 44 countries. The United States, the Soviet Union, the Netherlands and France received the largest plots, each about 25,000 square meters. The American and Soviet pavilions faced each other near the Atomium, and the Cold War rivalry shaped both. The Soviet Union displayed a replica of Sputnik and Laika's cabin, projecting technological mastery. The United States pavilion, designed by Edward Durell Stone with displays by Peter G. Harnden and Bernard Rudofsky, stood under a translucent, cable-tensioned roof and included a Circarama theater showing a 360-degree Walt Disney film tour of the United States, as well as "Unfinished Work," an exhibit on the country's social and racial problems. The Czechoslovak pavilion introduced Laterna Magika, a new form of immersive theater.

The Atomium became the Expo's symbol. Designed by engineer André Waterkeyn with architects André and Jean Polak, the 102-meter structure represents the unit cell of an iron crystal enlarged 165 billion times, with nine spheres joined by tubes. It was completed on March 25, 1958, at a cost of 200 million Belgian francs, and its upper sphere held a restaurant. Nearby, the Philips Pavilion, commissioned by Philips artistic director Louis Kalff, was designed by Le Corbusier in collaboration with Iannis Xenakis and Edgar Varèse as the setting for the multisensory “Poème électronique.” The Arrow of Civil Engineering, a reinforced concrete structure about 80 meters long by Jean Van Doosselaere, André Paduart and Jacques Moeschal, carried visitors over a relief map of Belgium. Many buildings broke with symmetry in favor of angles and curves, a manner later known as the "58 style."

The Expo reused the grounds of Expo 1935 Brussels and extended into Laeken park by way of a precast concrete footbridge. The Centenary Palace received a temporary new facade, and a new hall, Palace No. 7, added 10,000 square meters of exhibition space. The city itself was reshaped for cars and air travel: urban motorways were built, Zaventem airport was developed, and a new tram line carried visitors from the city center to the site. The Cité Modèle housing project in Laeken, begun in this period, was not completed until the 1960s.

Belgium also used the Expo to present its colony in the Congo. Seven pavilions covered Congolese mining, arts, transport and agriculture, and in the tropical gardens organizers set up a "typical" village where Congolese people were put on display. The Brussels Times has described this section as one of the darkest aspects of the event, and the Atomium's own history calls the colonial section "somewhat controversial."

Most pavilions were demolished or moved after the closing. The Austrian pavilion was rebuilt as a museum in Vienna and the Czechoslovak pavilion in Prague, while parts of the United States pavilion were taken over in 1961 by the Belgian broadcaster NIR, today's VRT, which still uses them. The Centenary Palace complex became the Brussels Exhibition Centre. The Atomium, intended to stand only for six months, was kept, renovated between 2004 and 2006, and now houses an exhibition on Expo 58. Expo 1958 Brussels gave Belgium its best-known modern landmark and remains a vivid record of postwar faith in science, set against the tensions of the Cold War and the end of the colonial era.