Carlos Castillo Armas (locally ['kaɾlos kas'tiʝo 'aɾmas]; 4 November 1914 – 26 July 1957) was a Guatemalan military officer and politician who was the 28th president of Guatemala, serving from 1954 to 1957 after taking power in a coup d'état. A member of the right-wing National Liberation Movement (MLN) party, his authoritarian government was closely allied with the United States.

Born to a planter, out of wedlock, Castillo Armas was educated at Guatemala's military academy. A protégé of Colonel Francisco Javier Arana, he joined Arana's forces during the 1944 uprising against President Federico Ponce Vaides. This began the Guatemalan Revolution and the introduction of representative democracy to the country. Castillo Armas joined the General Staff and became director of the military academy. Arana and Castillo Armas opposed the newly elected government of Juan José Arévalo; after Arana's failed 1949 coup, Castillo Armas went into exile in Honduras. Seeking support for another revolt, he came to the attention of the US Central Intelligence Agency (CIA). In 1950 he launched a failed assault on Guatemala City, before escaping back to Honduras. Influenced by lobbying by the United Fruit Company and Cold War fears of communism, in 1952 the US government of President Harry Truman authorized Operation PBFortune, a plot to overthrow Arévalo's successor, President Jacobo Árbenz. Castillo Armas was to lead the coup, but the plan was abandoned before being revived in a new form by US President Dwight D. Eisenhower in 1953.

In June 1954, Castillo Armas led 480 CIA-trained soldiers into Guatemala, backed by US-supplied aircraft. Despite initial setbacks to the rebel forces, US support for the rebels made the Guatemalan army reluctant to fight, and Árbenz resigned on 27 June. A series of military juntas briefly held power during negotiations that ended with Castillo Armas assuming the presidency on 7 July. Castillo Armas consolidated his power in an October 1954 election, in which he was the only candidate; the MLN, which he led, was the only party allowed to contest the congressional elections. Árbenz's popular agricultural reform was largely rolled back, with land confiscated from small farmers and returned to large landowners. Castillo Armas cracked down on unions and peasant organizations, arresting and killing thousands. He created a National Committee of Defense Against Communism, which investigated over 70,000 people and added 10 percent of the population to a list of suspected communists.

Castillo Armas faced significant internal resistance, which was blamed on communist agitation. The government, plagued by corruption and soaring debt, became dependent on aid from the US. In 1957 Castillo Armas was assassinated by a presidential guard with leftist sympathies. He was the first of a series of authoritarian rulers in Guatemala who were close allies of the US. His reversal of the reforms of his predecessors sparked a series of leftist insurgencies in the country after his death, culminating in the Guatemalan Civil War of 1960 to 1996.