“International Ocean Exposition, Okinawa 1975” was held in Okinawa, Japan, from July 20, 1975, to January 18, 1976. Organized by the Expo '75 Association and recognized by the International Exhibitions Bureau (Bureau International des Expositions, BIE) as a special exhibition, it marked the return of Okinawa to Japanese administration in 1972. Its theme was "The Sea We Would Like to See." Over 183 days, the Expo recorded 3,485,750 visits.

Following the success of Expo 1970 Osaka, the Japanese government chose Okinawa as host to help address the inequality between the islands and the rest of the country and to mark their reversion to Japan. The BIE General Assembly recognized the Expo at its 71st session on May 25, 1972, and the Japanese Ocean Expo Association approved the master plan that October. Concerns over the oil crisis delayed the opening by four months. Historian Vivian Blaxell has argued that the Expo was designed to give visible form to Japanese sovereignty in Okinawa, where the U.S. military presence continued after reversion.

According to Japan's Ministry of Foreign Affairs, 36 countries, including Japan, and three international organizations took part. Rather than building their own pavilions, participants rented prefabricated modules of about 250 square meters, either rectangular or hexagonal. The Soviet pavilion presented the first large-scale map of the ocean, while the United States pavilion, one of the largest, included a demonstration of ocean thermal power and research on the interaction between air and sea. The grounds were organized in four thematic clusters: People and History, Science and Technology, Fish and Ship. A water-themed amusement area, Expo Land, offered attractions such as canoeing through a waterfall.

The centerpiece was Aquapolis, a floating structure designed by architect Kiyonori Kikutake as a prototype marine community. Officially the Floating Pavilion of the Government of Japan, it was built at Mitsubishi's Hiroshima shipyard and towed about 1,000 kilometers to Motobu. The BIE puts its cost at 14 billion yen. Aquapolis remained in operation until 1993 and was scrapped in Shanghai in 2000.

The Expo brought motorways, water supply systems, and hotels to Okinawa and helped improve the island's image after decades of U.S. control. It did not reach its visitor target, however, and Blaxell notes that much of the estimated 180 billion yen in government spending went to mainland construction firms rather than to Okinawans.

The site became the Okinawa Commemorative National Government Park, known as Ocean Expo Park. It includes the Oceanic Culture Museum, a museum of native Okinawan life, a tropical and subtropical arboretum, and the Okinawa Churaumi Aquarium, which opened in November 2002 and holds 7,500 cubic meters of seawater in its main tank. Expo 1975 Okinawa tied the islands' return to Japan to a vision of humanity's future with the sea, and its park keeps that connection alive.