The Gregorian calendar date of the October Revolution, which gets its name from the Julian calendar date of 25 October. On this date in 1917, the Bolsheviks storm the Winter Palace.

The Winter Palace (Russian: , tr. Zimnij dvorets, IPA: [zimnj dvrts]) is a palace in Saint Petersburg that served as the official residence of the Russian Emperor from 1732 to 1917. The palace and its precincts now house the Hermitage Museum. Situated between Palace Embankment and Palace Square, adjacent to the site of Peter the Great's original Winter Palace, the present and fourth Winter Palace was built and altered almost continuously between the late 1730s and 1837, when it was severely damaged by fire and immediately rebuilt. The storming of the palace in 1917, as depicted in Soviet art and in Sergei Eisenstein's 1928 film October, became an iconic symbol of the Russian Revolution.

The emperors constructed their palaces on a monumental scale that aimed to reflect the might and power of Imperial Russia. From the palace, the tsars ruled over 22,800,000 square kilometers (8,800,000 sq mi) (almost 1/6 of the Earth's landmass) and 125 million subjects by the end of the 19th century. Several architects participated in designing the Winter Palacemost notably the Italian Bartolomeo Rastrelli (17001771)in what became known as the Elizabethan Baroque style. The green-and-white palace has the overall shape of an elongated rectangle, and its principal faade is 215 metres (705 ft) long and 30 m (98 ft) high. The Winter Palace has been calculated to contain 1,886 doors, 1,945 windows, 1,500 rooms and 117 staircases. Following a serious fire, the palace's rebuilding of 1837 left the exterior unchanged, but large parts of the interior were redesigned in a variety of tastes and styles, leading the palace to be described as a "19th-century palace inspired by a model in Rococo style".In 1905 the Bloody Sunday massacre occurred when demonstrators marched toward the Winter Palace, but by this time the Imperial Family had chosen to live in the more secure and secluded Alexander Palace at Tsarskoe Selo (lit. "regal village"), and returned to the Winter Palace only for formal and state occasions. Following the February Revolution of 1917, the palace operated for a short time as the seat of the Russian Provisional Government, ultimately led by Alexander Kerensky. Later that same year a detachment of Red Guard soldiers and sailors stormed the palacea defining moment in the birth of the Soviet state.

The October Revolution, officially known as the Great October Socialist Revolution under the Soviet Union, also known as the Bolshevik Revolution, was a revolution in Russia led by the Bolshevik Party of Vladimir Lenin that was instrumental in the larger Russian Revolution of 1917–1923. It was the second revolutionary change of government in Russia in 1917. It took place through an armed insurrection in Petrograd (now Saint Petersburg) on 7 November 1917 [O.S. 25 October]. It was the precipitating event of the Russian Civil War.

The October Revolution followed and capitalized on the February Revolution earlier in the year. The February Revolution had overthrown the Tsarist autocracy, resulting in a provisional government. The provisional government had taken power after being proclaimed by Grand Duke Michael, Tsar Nicholas II's younger brother, who declined to take power after the Tsar stepped down. During this time, urban workers began to organize into councils (soviets) wherein revolutionaries criticized the provisional government and its actions. The provisional government's popularity imploded largely due to their decision to remain in World War I. To prevent further insurrections the Provisional Government began ruling with an iron fist throughout the summer which resulted in the deaths of hundreds of protesters in the July Days.

The July Days coupled with widespread anti-war sentiment contributed to the Bolsheviks' rising popularity. Using this popularity, the Bolsheviks pressured the Directorate, led by the left-wing Socialist Revolutionary Party, to give into their demands. When this approach failed, the Bolsheviks began spreading calls for a military uprising. On 10 October 1917 (O.S.; 23 October, N.S.), the Petrograd Soviet, led by Trotsky, voted to back a military uprising. On 24 October (O.S.; 6 November, N.S.) the government shut down numerous newspapers and closed the city of Petrograd in an attempt to forestall the revolution; minor armed skirmishes broke out. The next day a full scale uprising erupted, as a fleet of Bolshevik sailors entered the harbor and tens of thousands of soldiers rose up in support of the Bolsheviks. Bolshevik Red Guards forces under the Military-Revolutionary Committee began the occupation of government buildings on 25 October (O.S.; 7 November, N.S.), 1917. The following day, the Winter Palace (the seat of the Provisional government located in Petrograd, then capital of Russia) was captured.

As the Revolution was not universally recognized, the country descended into civil war, which would last until 1923. The Bolsheviks having won the civil war, reconstituted the former Russian Empire into the Soviet Union in late 1922. Historiographical descriptions of the event have been widely varied since 1917. The victorious Bolsheviks viewed it as a validation of their ideology, and the triumph of the worker over capitalism. On the other hand, the Western powers saw it as a coup, where the Bolsheviks replaced the democratically controlled workers' Soviets with a totalitarian dictatorship.

During Soviet times, revolution day was made a national holiday, marking its importance in the country's founding story. The event inspired many cultural works, and ignited communist movements across Europe and globally. Many Marxist–Leninist parties around the world still celebrate revolution day. Contemporary Russia distanced itself from its Soviet past by removing the October Revolution as a national holiday.