The “Century 21 Exposition” was held in Seattle, Washington, United States, from April 21 to October 21, 1962. Organized by the City of Seattle, the State of Washington and the U.S. government, it was a general exhibition of the second category under the 1928 Paris Convention. The International Exhibitions Bureau (Bureau International des Expositions, BIE) records 9 million visits on a 30-hectare site; city records put the total at more than 10 million.

The idea came from Seattle City Councilman Al Rochester, who had attended the 1909 Alaska-Yukon-Pacific Exposition as a boy and proposed a second exposition to commemorate it. A 1955 state law funded a World's Fair Commission chaired by hotel executive Eddie Carlson, with Rochester as executive director; Joe Gandy later succeeded Carlson and served as the Expo's president. Seattle voters approved a $7.5 million Civic Center bond, which the state legislature matched, and the U.S. government contributed more than $9 million, mainly for its science exhibit. BIE approval, which Gandy won despite a competing project in New York, helped the organizers recruit 35 foreign governments as exhibitors.

The theme, "Man in the Space Age," looked ahead to life in the 21st century at a moment when the space race dominated public imagination. President John F. Kennedy opened the Expo on April 21, 1962. The BIE lists 49 participants, and international exhibits came from countries including Canada, India, Japan, Sweden, France and the United Arab Republic. The Soviet Union did not exhibit, although cosmonaut Gherman Titov visited.

Architect Paul Thiry, named chief architect in 1958, planned the grounds and designed the Washington State Coliseum, whose suspended roof sheltered the state's pavilion. Minoru Yamasaki designed the U.S. Science Pavilion, blending Japanese and Gothic forms around a NASA-themed exhibit; Boeing's Spacearium was its most popular attraction. Tokyo architects Hideki Shimizu and Kazuyuki Matsushita designed the International Fountain, dedicated on May 31, 1962.

The Space Needle became the Expo's symbol. Carlson sketched the idea on a napkin after dining atop a television tower in Stuttgart, Germany, and Victor Steinbrueck and John Ridley developed the design of a tripod crowned by a disc. Built in about a year, the 605-foot tower offered an elevator ride for $1.

To link the grounds with downtown, the city contracted Alweg Rapid Transit Systems for a monorail that ran 1.3 miles along Fifth Avenue; the trip took 95 seconds. The city also built a 1,500-car garage and moved about 3.5 miles of overhead lines underground. Gandy closed the Expo on October 21, 1962, at Memorial Stadium. Kennedy had been expected but sent regrets, citing a cold, while he was in fact facing the early days of the Cuban Missile Crisis.

The grounds became Seattle Center, a 74-acre campus that hosts more than 30 arts, culture, sports and entertainment organizations. The Coliseum is now Climate Pledge Arena, which kept its original roof and framework, and the U.S. Science Pavilion is the Pacific Science Center. The Space Needle became a City of Seattle landmark in 1999, and the monorail and its tracks received landmark status in 2003. The monorail still carries riders between Seattle Center and downtown.

Expo 1962 Seattle brought the city international recognition and gave it a civic center that remains in daily use. Its vision of the Space Age, captured in the Space Needle, endures as one of the most recognizable legacies of any Expo.