The Kronstadt rebellion (Russian: Кронштадтское восстание, romanized: Kronshtadtskoye vosstaniye) was a 1921 insurrection of Soviet sailors, naval infantry, and civilians against the Bolshevik government in the Russian port city of Kronstadt. Located on Kotlin Island in the Gulf of Finland, Kronstadt defended the former capital city, Petrograd (now Saint Petersburg), as the base of the Baltic Fleet. For sixteen days in March 1921, rebels in Kronstadt's naval fortress rose in opposition to the Soviet government which they had helped to consolidate. Led by Stepan Petrichenko, it was the last major revolt against Bolshevik rule on Russian territory during the Russian Civil War.

Disappointed in the direction of the Bolshevik government, the rebels—whom Leon Trotsky himself had praised earlier as the "adornment and pride of the revolution"—demanded a series of reforms: reduction in Bolshevik power, newly elected soviets (councils) to include socialist and anarchist groups, economic freedom for peasants and workers, dissolution of the bureaucratic governmental organs created during the civil war, and the restoration of civil rights for the working class. Trotsky signed the order to crush the rebellion which outlined a series of operational measures including a warning to the sailors to stop the rebellion in advance of a Red Army assault. However, he did not personally participate in the military operations or repressions which were organized by Felix Dzerzhinsky.

Convinced of the popularity of the reforms they were fighting for (which they partially tried to implement during the revolt), the Kronstadt seamen waited in vain for the support of the population in the rest of the country and rejected aid from the emigres. Although the council of officers advocated a more offensive strategy, the rebels maintained a passive attitude as they waited for the government to take the first step in negotiations. By contrast, the authorities took an uncompromising stance, presenting an ultimatum demanding unconditional surrender on March 5. Once this period expired, the Bolsheviks raided the island several times and suppressed the revolt on March 18 after shooting and imprisoning several thousand rebels.

Supporters saw the rebels as revolutionary martyrs while the authorities saw the rebels as "agents of the Entente and counter-revolution". The Bolshevik response to the revolt caused great controversy and was responsible for the disillusionment of several supporters of the Bolshevik regime, such as Emma Goldman. While the revolt was suppressed and the rebels' political demands were not met, it served to accelerate the implementation of the New Economic Policy, which replaced war communism. According to Lenin, the crisis was the most critical the Bolsheviks had yet faced, "undoubtedly more dangerous than Denikin, Yudenich, and Kolchak combined".

As the Russian Civil War wound down in late 1920, the Bolsheviks presided over a nation in ruin. Their communist Red Army had defeated Pyotr Wrangel's anti-communist White Army, and was militarily equipped to suppress outstanding peasant insurrections, but faced mass disillusionment from unbearable living conditions—famine, disease, cold, and weariness—induced by the years of war and exacerbated by the Bolshevik policy of war communism. Peasants had started to resent government requisitions of grain, with seizures of their already meager harvest being coupled with cutbacks on bread rations and a fuel shortage.

Despite military victory and stabilized foreign relations, Russia faced a serious social and economic crisis. As foreign troops began to withdraw, Bolshevik leaders continued to sustain tight control of the economy through the policy of war communism. Discontent grew among the Russian populace, particularly the peasantry, who felt disadvantaged by government grain requisitioning (prodrazvyorstka, the forced seizure of large portions of the peasants' grain crop used to feed urban dwellers). In resistance of these policies, peasants began refusing to till their farms. In February 1921, the Cheka reported 155 peasant uprisings across Russia. The workers in Petrograd were also involved in a series of strikes, caused by the reduction of bread rations by one third over a ten-day period. With this information and already stoked discontent, the revolt at the Kronstadt naval base began as a protest over the plight of the country. Agricultural and industrial production had been drastically reduced and the transport system was disorganized.

The arrival of winter and the maintenance of "war communism" and various deprivations by Bolshevik authorities led to increased tensions in the countryside (as in the Tambov Uprising) and in the cities, especially Moscow and Petrograd—where strikes and demonstrations took place—in early 1921. Due to the maintenance and reinforcement of "war communism", living conditions worsened even more after the fighting ended.

Protests followed a January 1921 announcement in which the government reduced bread rations by one third for inhabitants of all cities. While this decision was forced, between heavy snow and fuel shortages preventing stored food transport in Siberia and the Caucasus, this justification did not prevent popular discontent. In mid-February, workers began to rally in Moscow; such demonstrations were preceded by workers' meetings in factories and workshops. The workers demanded the end of "war communism" and a return to free labor. The government's representatives could not alleviate the situation, and it quickly decided that the revolts could only be suppressed by armed troops.