Tenentism (Portuguese: tenentismo) was a political philosophy of junior army officers (tenentes, IPA: [teˈnẽtʃis], "lieutenants"), generally from the burgeoning middle-class and unsatisfied with the oligarchic structure of the republic who significantly contributed to the Brazilian Revolution of 1930 that ended the First Brazilian Republic.

The movement advocated reforms in the country's power structure, among which the end of open ballot system (the end of the so-called vote of cabresto), a voting method that favored the coronelismo present in the Oligarchic Republic, in addition to defending the institution of Secret ballots, universal suffrage and reform in public education.

The first decades of the 20th century saw marked economic and social change in Brazil. With industrialization on the rise, the federal government — dominated by the coffee oligarchs and the old order of café com leite politics and coronelismo — came under threat from the political aspirations of new urban groups: the proletariat, government and white-collar workers, merchants, bankers, and industrialists. In parallel, growing prosperity encouraged a rapid rise of a new working class of Southern and Eastern European immigrants who contributed to the growth of trade unionism, anarchism, and socialism in Brazil. In the post-World War I period, Brazil saw its first wave of general strikes and the establishment of the Communist Party in 1922.

A new class of junior army officers (Portuguese: tenentes) had emerged. They were trained in European war standards and believed themselves superior to their senior officers who still held antiquated ideas of the past. In addition, various senior officers had become complacent or sided with the government and its political structure, which sparked criticism from the tenentes.

Meanwhile, the divergence of interests between the coffee oligarchs and the burgeoning, dynamic urban sectors was intensifying. According to historian Benjamin Keen, the task of transforming society "fell to the rapidly growing urban bourgeois groups, and especially to the middle class, which began to voice even more strongly its discontent with the rule of the corrupt rural oligarchies". In contrast, despite a wave of general strikes in the post-war years, the labour movement remained small and weak, lacking ties to the peasantry, who constituted the overwhelming majority of the Brazilian population. As a result, rather disparate and disjointed social reform movements cropped up in the 1920s.

What became known as the tenentist movement came to public notice on 5 July 1922 when a group of young army officers began a rebellion against the First Brazilian Republic at Fort Copacabana in Rio de Janeiro. Sparked initially by the punishment and brief imprisonment of marshal Hermes da Fonseca by president Epitácio Pessoa, the tenentes attempted to prevent Artur Bernardes, winner of the 1922 presidential election, from taking office. The tenentes demanded various forms of social modernization, calling for agrarian reform, the formation of cooperatives, and the nationalization of mines.

Their early-morning rebellion was taken up by a garrison in São Paulo but not by others; only "scattered units around Rio de Janeiro revolted: the Escola Militar, some elements of the First Infantry Regiment and the Battalion of Engineers, and the garrisons of Forts Copacabana and Vigia. However, the remainder of the First Army Division stayed loyal and, with General Setembrino de Carvalho supervising the operations, easily crushed the revolt". Twenty-four hours later, just 200 rebels remained when the navy dreadnought Minas Geraes shelled the Copacabana barracks, after which two navy aircraft bombed the barracks in the first use of naval aircraft in combat in Latin America. The defenders were driven from their positions. A group known subsequently as the 18 of the Copacabana Fort revolt were led down Avenida Atlântica by Antônio de Siqueira Campos and Eduardo Gomes to confront the army loyalists; the eighteen made a last stand on the beach, where sixteen were killed and two, Gomes and Campos, survived. In the aftermath, the government imposed a state of emergency, 1,000 cadets were expelled from the army school and many officers were sent to remote garrisons.

The São Paulo Revolt of 1924 was the second tenentist revolt and the largest conflict in the city of São Paulo. It began in the early hours of July 5 and ended on 28 July 1924. The revolt was motivated by the discontent of the military with the economic crisis and the concentration of power at the hands of politicians from São Paulo and Minas Gerais. Commanded by retired General Isidoro Dias Lopes, with the participation of several lieutenants, the main objective of the uprising was to depose President Artur Bernardes (considered to be an enemy of the military since the crisis of the fake letters). Among the demands was the adoption of the secret ballot, free justice and the introduction of compulsory public education.