The Russian Revolution was a period of political and social change in Russia, starting in 1917. This period saw Russia abolish its monarchy and adopt a socialist form of government following two successive revolutions and a civil war. It can be seen as the precursor for other revolutions that occurred in the aftermath of World War I, such as the German Revolution of 1918–1919. The Russian Revolution was a key event of the 20th century.

The Russian Revolution was inaugurated with the February Revolution in 1917, in the midst of World War I. With the German Empire inflicting defeats on the front, and increasing logistical problems causing shortages of bread and grain, the Russian Army was losing morale, with large scale mutiny looming. Officials were convinced that if Tsar Nicholas II abdicated, the unrest would subside. Nicholas stepped down on 15 March [O.S. 2 March], ushering in a provisional government led by the Duma (parliament). During the unrest, Soviet councils were formed by locals in Petrograd that initially did not oppose the new government; however, the Soviets insisted on their influence in the government and control over militias. By March, Russia had two rival governments. The Provisional Government held state power in military and international affairs, whereas the network of Soviets held domestic power. Critically, the Soviets held the allegiance of the working class, and urban middle class. There were mutinies, protests and strikes. Socialist and other leftist political organizations competed for influence within the Provisional Government and Soviets. Factions included the Mensheviks, Social Revolutionaries, Anarchists, and the Bolsheviks, a far-left party led by Vladimir Lenin.

The Bolsheviks won popularity with their program promising peace, land, and bread: an end to the war, land for the peasantry, and ending famine. After assuming power, the Provisional Government continued fighting the war in spite of public opposition. Taking advantage, the Bolsheviks and other factions gained popular support to advance the revolution. Responding to discontent in Petrograd, the Provisional Government repressed protestors leading to the July Days. The Bolsheviks merged workers' militias loyal to them into the Red Guards. The volatile situation reached its climax with the October Revolution, a Bolshevik armed insurrection in Petrograd beginning 7 November [O.S. 25 October] that overthrew the Provisional Government. The Bolsheviks established their own government and proclaimed the establishment of the Russian Soviet Federative Socialist Republic (RSFSR). Under pressure from German military offensives, the Bolsheviks relocated the capital to Moscow. The RSFSR began reorganizing the empire into the world's first socialist state, to practice soviet democracy on a national and international scale. Their promise to end Russia's participation in World War I was fulfilled when Bolshevik leaders signed the Treaty of Brest-Litovsk with Germany in March 1918. The Bolsheviks established the Cheka, a secret police and revolutionary security service working to uncover, punish, and eliminate those considered to be "enemies of the people" in campaigns called the Red Terror.

Although the Bolsheviks held large support in urban areas, they had foreign and domestic enemies that refused to recognize their government. Russia erupted into a bloody civil war, which pitted the Reds (Bolsheviks), against their enemies, which included nationalist movements, anti-Bolshevik socialist parties, anarchists, monarchists and liberals; the latter two parties strongly supported the Russian White movement which was led mainly by right-leaning officers and seen as fighting for the restoration of the imperial order. The Bolshevik commissar Leon Trotsky began organizing workers' militias loyal to the Bolsheviks into the Red Army. While key events occurred in Moscow and Petrograd, every city in the empire was convulsed, including the provinces of national minorities, and in the rural areas peasants took over and redistributed land.

As the war progressed, the RSFSR established Soviet power in Armenia, Azerbaijan, Byelorussia, Georgia, and Ukraine. Wartime cohesion and intervention from foreign powers prompted the RSFSR to begin unifying these nations under one flag and created the Soviet Union. Historians consider the end of the revolutionary period to be in 1922, when the civil war concluded with the defeat of the White Army and separatist factions, leading to mass emigration from Russia. The victorious Bolshevik Party reconstituted itself into the All-Union Communist Party (Bolsheviks) and remained in power for six decades.

The Russian Revolution of 1905 was a major factor contributing to the cause of the Revolutions of 1917. The events of Bloody Sunday triggered nationwide protests and soldier mutinies. A council of workers called the St. Petersburg Soviet was created in this chaos. While the 1905 Revolution was ultimately crushed, and the leaders of the St. Petersburg Soviet were arrested, this laid the groundwork for the later Petrograd Soviet and other revolutionary movements during the leadup to 1917. The 1905 Revolution also led to the creation of a Duma (parliament) that would later form the Provisional Government following February 1917.

Russia's poor performance in 1914–1915 prompted growing complaints directed at Tsar Nicholas II and the Romanov family. A short wave of patriotic nationalism ended in the face of defeats and poor conditions on the Eastern Front of World War I. The Tsar made the situation worse by taking personal control of the Imperial Russian Army in 1915, a challenge far beyond his skills. He was now held personally responsible for Russia's continuing defeats and losses. In addition, Tsarina Alexandra, left to rule while the Tsar commanded at the front, was German born, leading to suspicion of collusion, only to be exacerbated by rumors relating to her relationship with the controversial mystic Grigori Rasputin. Rasputin's influence led to disastrous ministerial appointments and corruption, resulting in a worsening of conditions within Russia.

After the entry of the Ottoman Empire on the side of the Central Powers in October 1914, Russia was deprived of a major trade route to the Mediterranean Sea, which worsened the economic crisis and the munitions shortages. Meanwhile, Germany was able to produce great amounts of munitions whilst constantly fighting on two major battlefronts.