The Sandinista National Liberation Front (Spanish: Frente Sandinista de Liberación Nacional, FSLN) is a socialist political party in Nicaragua. Its members are called Sandinistas (Spanish pronunciation: [sandiˈnistas]) in both English and Spanish. The party is named after Augusto César Sandino, who led the Nicaraguan resistance against the United States occupation of Nicaragua in the 1930s.

The FSLN overthrew Anastasio Somoza Debayle in the 1979 Nicaraguan Revolution, ending the Somoza dynasty, and established a revolutionary government in its place. Having seized power, the Sandinistas ruled Nicaragua from 1979 to 1990, first as part of a Junta of National Reconstruction. Following the resignation of centrist members from this Junta, the FSLN took exclusive power in March 1981. They instituted a policy of mass literacy while devoting significant resources to health care, but came under international criticism for human rights abuses, mass execution and oppression of indigenous peoples.

A US-backed group, known as the Contras, was formed in 1981 to overthrow the Sandinista government and was funded and trained by the Central Intelligence Agency. In 1984 elections were held but were boycotted by opposition parties. The FSLN won the majority of the votes, and those who opposed the Sandinistas won approximately a third of the seats. The civil war between the Contras and the government continued until 1989. After revising the constitution in 1987, and after years of fighting the Contras, the FSLN lost the 1990 election to Violeta Barrios de Chamorro but retained a plurality of seats in the legislature. The FSLN is now Nicaragua's sole leading party. In the 2006 Nicaraguan general election, former FSLN President Daniel Ortega was reelected President of Nicaragua with 38.7% of the vote to 29% for his leading rival, bringing in the country's second Sandinista government after 17 years of other parties winning elections. Ortega and the FSLN were reelected in the presidential elections of 2011, 2016, and 2021.