The Itaipu Dam (Guarani: Yjoko Itaipu [itajˈpu]; Portuguese: Barragem de Itaipu [itajˈpu]; Spanish: Represa de Itaipú [itajˈpu]) is a hydroelectric dam on the Paraná River located on the border between Brazil and Paraguay. It is the third-largest hydroelectric dam in the world in terms of produced energy.

The name "Itaipu" was taken from an island that existed near the construction site. In the Guarani language, Itaipu means "the sounding stone." As of 2020, the Itaipu Dam's hydroelectric power plant produced the second-largest amount of electricity of any hydroelectric power plant in the world, with its electricity production being only surpassed by the Three Gorges Dam plant in China. Additionally, Itaipu also holds the 45th largest reservoir in the world.

With its construction completed in 1984, it is a binational undertaking run by Brazil and Paraguay at the border between the two countries, 15 km (9.3 mi) north of the Friendship Bridge. The project ranges from Foz do Iguaçu, in Brazil, and Ciudad del Este in Paraguay, in the south to Guaíra and Salto del Guairá in the north. The installed generation capacity of the plant is 14 GW, with 20 generating units providing 700 MW each with a hydraulic design head of 118 metres (387 ft). In 2016, the plant employed 3038 workers.

Of the twenty generator units currently installed, ten generate at 50 Hz for Paraguay and ten generate at 60 Hz for Brazil. Since the output capacity of the Paraguayan generators far exceeds the load in Paraguay, most of their production is exported directly to the Brazilian side, from where two 600 kV HVDC lines, each approximately 800 kilometres (500 mi) long, carry the majority of the energy to the São Paulo/Rio de Janeiro region where the terminal equipment converts the power to 60 Hz.

The concept behind the Itaipu Power Plant was the result of serious negotiations between the two countries during the 1960s. The "Ata do Iguaçu" (Iguaçu Act) was signed on July 22, 1966, by the Brazilian and Paraguayan Ministers of Foreign Affairs, Juracy Magalhães and Raúl Sapena Pastor. This was a joint declaration of the mutual interest in studying the exploitation of the hydro resources that the two countries shared in the section of the Paraná River starting from and including the Salto de Sete Quedas, to the Iguaçu River watershed. The treaty that gave origin to the power plant was signed in 1973.

The terms of the treaty, which expired in 2023, have been the subject of widespread discontent in Paraguay. The government of President Lugo vowed to renegotiate the terms of the treaty with Brazil, which long remained hostile to any renegotiation.

In 2009, Brazil agreed to a fairer payment of electricity to Paraguay and also allowed Paraguay to sell excess power directly to Brazilian companies instead of solely through the Brazilian electricity monopoly.

In 1970, the consortium formed by the companies ELC Electroconsult S.p.A. (from Italy) and IECO (from the United States) won the international competition for the realization of the viability studies and for the elaboration of the construction project. Design studies began in February 1971. On April 26, 1973, Brazil and Paraguay signed the Itaipu Treaty, the legal instrument for the hydroelectric exploitation of the Paraná River by the two countries. On May 17, 1974, the Itaipu Binacional entity was created to administer the plant's construction. The construction began in January of the following year. Brazil's (and Latin America's) first electric car was introduced in late 1974; it received the name Itaipu in honor of the project.