Ana Belén Montes (born February 28, 1957) is an American former senior analyst at the United States Defense Intelligence Agency who spied on behalf of the Cuban government for 17 years.

Montes was arrested on September 21, 2001, and she subsequently was charged with conspiracy to commit espionage for the government of Cuba. Montes pleaded guilty to spying and, in October 2002, was sentenced to a 25-year prison term to be followed by five-years' probation. She was released on January 6, 2023, after having served 20 years behind bars.

Montes's family originated from the Asturian region of Spain, and her grandparents immigrated to Puerto Rico. She was born on February 28, 1957, at the U.S. Army Hospital in Nuremberg, West Germany, where her father, Alberto Montes, was posted as a U.S. Army doctor. Sixteen months later, her younger sister Luz, nicknamed Lucy, was born at the same Army hospital. The family moved to the United States on August 26, 1958, following the completion of Alberto's three-year posting, and by the fall of that year, they were living in Topeka, Kansas, where Montes's younger brother Alberto, nicknamed Tito, was born in June 1959. In 1967, the family relocated to Towson, Maryland, where Montes graduated from Loch Raven High School in 1975. The Montes children reportedly experienced physical and emotional abuse from their father throughout their upbringing.

In 1975, Montes enrolled at the University of Virginia in Charlottesville, where she initially majored in history. Two years later, she changed her major to foreign affairs and spent her junior year studying abroad in Spain through the Institute of European Studies. During her time in Spain in 1977, she met Ricardo Fernandez Eiriz, a leftist from Argentina, with whom she began a relationship. Eiriz spoke with Montes about U.S. support for authoritarian governments, conversations that played a major role in shaping her political outlook.

During her year in Spain, as the country transitioned to democracy following the death of dictator Francisco Franco, Montes participated in street rallies with friends amid widespread anti-U.S. sentiment over American support for Franco. She wrote letters to her sister Lucy expressing a growing interest in Cuba and began identifying as a leftist. Although her relationship with Eiriz ended after her time abroad, a later report by the Department of Defense Office of Inspector General stated that she had become "attracted to the social Communist parties in Europe during her junior academic year in Spain in 1978."

Montes graduated in 1979 and moved to Puerto Rico, where she worked as a receptionist at a law firm before taking a temporary position at the Universidad del Sagrado Corazón in San Juan. In December 1979, she relocated to Washington, D.C., after learning of a job opening as a clerk-typist with the United States Department of Justice (DOJ) in its Office of Privacy and Information Appeals. This position marked the beginning of her twenty-two–year career in the U.S. government. The Federal Bureau of Investigation (FBI) conducted a routine background check on Montes but did not uncover her increasing disillusionment with the U.S. government. She quickly gained a strong reputation at the Justice Department and, after three years, was promoted to paralegal.

In 1982, while working at the Justice Department, Montes began a two-year master's program at Johns Hopkins University's School of Advanced International Studies (SAIS), concentrating in Latin American studies, where she connected with other leftists who shared her increasingly radical views. During her time at SAIS, she met fellow graduate student Marta Velázquez, who was described by acquaintances as politically leftist. Velázquez had studied political science and Latin American studies at Princeton University beginning in 1975, during which she traveled to Cuba to conduct field research for her senior thesis. She later earned a Juris Doctor degree from Georgetown University Law Center before enrolling at SAIS in the fall of 1982. According to the U.S. Justice Department, Velázquez became a Cuban agent in 1983 after traveling from Washington to Mexico City “to clandestinely meet with Cuban Intelligence Service officers and/or agents.” It is unclear how Cuban intelligence first established contact with her, though it is believed she may have been approached during her undergraduate trip to Cuba.

According to a grand jury indictment unsealed in 2013, the Justice Department stated that Velázquez assisted Cuban intelligence “in spotting, assessing, and recruiting United States citizens who occupied sensitive national security positions or had the potential of occupying such positions in the future—including Ana Belén Montes—to serve as agents of the Cuban intelligence service.” By 1984, Montes and Velázquez were closely associated and participated in the same SAIS graduation ceremony. Although Montes took part in the ceremony, she was handed an empty diploma because she still owed $2,300 in tuition, which she refused to pay, claiming the school had treated her unfairly and reneged on some financial aid. Later that year, on December 16, Montes attended a dinner in Manhattan with Velázquez and a Cuban intelligence officer. Defense Department investigators later reported that the twenty-seven-year-old Montes “unhesitatingly agreed to work through the Cubans to ‘help’ Nicaragua,” having already expressed moral opposition to U.S. policy in Nicaragua to Velázquez and others in class.