The Mariel boatlift (Spanish: éxodo del Mariel) was a mass emigration of Cubans who traveled from Cuba's Mariel Harbor to the United States between April 15 and October 31, 1980. The term "Marielito" is used to refer to these refugees in both Spanish and English. While the exodus was triggered by a sharp downturn in the Cuban economy, it followed on the heels of generations of Cubans who had immigrated to the United States in the preceding decades.

After 10,000 Cubans tried to gain asylum by taking refuge on the grounds of the Peruvian embassy, the Cuban government announced that anyone who wanted to leave could do so. The ensuing mass migration was organized by Cuban Americans, with the agreement of Cuban president Fidel Castro. The Cuban government considered the exodus a sort of social cleansing of the nations' so-called undesirables and organized acts of repudiation against prospective emigrants.

The arrival of the refugees in the United States created political problems for U.S. president Jimmy Carter. The Carter administration struggled to develop a consistent response to the immigrants. The Mariel boatlift was ended by mutual agreement between the two governments in late October 1980. By then, an estimated 125,000 Cubans had reached Florida.

In the late 1970s, U.S. president Jimmy Carter sought to improve relations with Cuba. He lifted all restrictions on travel to Cuba, and in September 1977, both countries established an Interests Section in each other's capital. However, relations were still strained because Cuba supported the Soviet Union's military interventions in Africa and the Middle East with their own. The two countries struggled to reach agreement on a relaxation of the US embargo on trade to permit the export of a select list of medicines to Cuba without provoking Carter's political opponents in the US Congress.

Ten members of Congress visited Cuba in December 1978, and the Cuban government later released Frank C. Emmick, the US manager of a business in Cuba who had been prevented from leaving in 1963, accused of being a CIA agent, and sentenced to 50 years in prison. A group of 55 people whose parents brought them from Cuba returned for three weeks in December 1978 in a rare instance of Cuba allowing the return of Cuban-born émigrés. In December 1978, both countries agreed upon their maritime border, and the next month, they were working on an agreement to improve their communications in the Straits of Florida. The US responded to Cuban relaxation of restrictions on emigration by allowing Cuban-Americans to send up to $500 to an emigrating relative (equal to $2,400 in 2023).

In November 1978, Castro's government met in Havana with a group of Cubans living in exile, agreed to grant an amnesty to 3,600 political prisoners, and announced that they would be freed in the course of the next year and allowed to leave Cuba.

Caribbean Holidays began offering one-week trips to Cuba in January 1978 in co-operation with Cubatur, the official Cuban travel agency. By May 1979, tours were being organized for Americans to participate in the Cuban Festival of Arts (Carifesta) in July, with flights departing from Tampa, Mexico City, and Montreal.

Before 1980, many Haitian immigrants arrived on American shores by boat. They were not granted legal protection because they were considered economic migrants, rather than political refugees, despite claims made by many Haitians that they were being persecuted by the Duvalier regime. U.S. presidents Richard Nixon and Gerald Ford denied claims of asylum in the United States for Haitian migrants by boat. A backlash by the Congressional Black Caucus ensued, which claimed that the U.S. government was discriminating against Haitian immigrants.