The Spanish coup of July 1936 was a military uprising against the Second Spanish Republic launched on 17–18 July 1936 by a coalition of conservative, monarchist, and far-right officers and civilians. Planned chiefly by Generals Emilio Mola and José Sanjurjo and joined by Francisco Franco, it was intended to overthrow the Popular Front government and replace it with an authoritarian regime. Instead of securing a rapid transfer of power, the coup only partially succeeded and precipitated the Spanish Civil War.

The rebellion began in Spanish Morocco on 17 July and spread to mainland garrisons the following day. It triumphed in parts of northern, western, and southern Spain, but failed in key political and industrial centres including Madrid, Barcelona, and Valencia. Because neither the rebels nor the government secured an immediate nationwide victory, Spain was divided between Nationalist and Republican zones. The government's decision to arm workers' organisations helped defeat the uprising in several major cities while also accelerating revolutionary change in parts of the Republican rear.

The failed coup transformed a political crisis into the Spanish Civil War, which lasted until 1939. It ended with the defeat of the Republic, the victory of Franco's Nationalists, and the establishment of the Franco dictatorship, which ruled Spain until 1975.

Following the elections of November 1933, Spain entered what was called by the left-wing parties the "black biennium" (Spanish: bienio negro). Both Carlists and Alfonsist monarchists continued to prepare and received the backing of Benito Mussolini. José-María Gil-Robles, the leader of the moderate-right Spanish Confederation of Autonomous Rights (CEDA), supported a centrist Radical Republican Party minority government and controlled his party's more radical youth wing. Monarchists, however, turned their attention to the fascist Falange Española, led by José Antonio Primo de Rivera. Open violence occurred in the streets of Spanish cities. Gil-Robles successfully used an anti-strike law to provoke and to break up unions, one at a time. Efforts to remove local councils from socialist control prompted a general strike, which was brutally put down, with the arrest of four deputies and other significant breaches of Articles 55 and 56 of the constitution.

On 26 September 1934, the minority government was replaced by a cabinet including the RRP and three CEDA members. A UGT general strike in early October 1934 was quickly put down throughout most of Spain. General Francisco Franco was put in informal command of the military effort against the Asturian miners' revolt of 1934, during which striking labourers had occupied several towns and the provincial capital. Around 30,000 workers had been called to arms in ten days. Franco's men, some brought in from Spain's Army of Africa, killed civilians, including men, women and children, and carried out summary executions when the main cities of Asturias were retaken. About 1,000 workers and about 250 government soldiers were killed, which marked the effective end of the republic. Months of retaliation and repression by both sides followed, and torture was used on political prisoners. Bombings, shootings, and political and religious killings were frequent in the streets. Political parties created armed militias. In 1935, a new government under prime minister Alejandro Lerroux saw CEDA increasing its share of ministries to five, with Gil-Robles becoming minister of war. The military was purged of left-wing members and reformed. Those loyal to Gil-Robles were promoted, and Franco was made chief of staff.

Contested under violent circumstances, the 1936 general election was narrowly won by a grouping of left-wing parties, the Popular Front, which defeated the Nationalist group by less than 1% of the vote. As a consequence, the Nationalists began to conspire to overthrow the Republic, rather than take control of it. The government was weak, Manuel Azaña led a minority government, and reconciliation would have been an enormous task. Acts of violence and reprisals spiralled. In April, the Cortes (parliament) replaced Niceto Alcalá-Zamora with Azaña as president, who, however, was increasingly isolated from everyday politics, and his replacement as prime minister, Casares Quiroga, was weak.

This development led much of the right to abandon parliamentary politics. The monarchist José Calvo Sotelo replaced CEDA's Gil-Robles as the leader of the right in the Cortes. CEDA turned its campaign chest over to the army plotter Emilio Mola. At the same time, communists quickly took over the ranks of socialist organisations, which frightened the middle classes. Several generals decided that the government had to be replaced to prevent the dissolution of Spain, as they held professional politicians in contempt.

Following the election of 18 January 1936, the Republican government in the winter and spring that year faced numerous challenges, not least of which was balancing itself between the threat posed by leftist unions, the counter for which might prove to be the continued support of the right-leaning military. As a consequence, Azaña had undertaken reassignment rather than dismissal of suspect generals from their posts. Franco was relieved as chief of staff and transferred to command the Canary Islands. Goded was replaced as Inspector General and made general of the Balearic Islands. Emilio Mola was moved from leading the Army of Africa to the post of military commander of Pamplona in Navarre. This allowed Mola to direct the mainland uprising, although the relationship between him and Carlist leaders was problematic. General José Sanjurjo became the figurehead of the operation and helped to come to an agreement with the Carlists. Mola was the chief planner and second in command. José Antonio Primo de Rivera was released from prison in mid-March to restrict the Falange. However, government actions were not as thorough as they might have been, since warnings by the director of security and others were not acted upon.