The Russian Empire was the final period of the Russian monarchy, spanning most of northern Eurasia from its establishment in November 1721 until the proclamation of the Russian Republic in September 1917. At its height in the late 19th century, it covered about 22,800,000 km2 (8,800,000 sq mi), roughly one-sixth of the world's landmass, making it the third-largest empire in history, behind only the British and Mongol empires. It also colonized Alaska between 1799 and 1867. The empire's 1897 census, the only one it conducted, found a population of 125.6 million with considerable ethnic, linguistic, religious, and socioeconomic diversity.

From the 10th to 17th century, the Russian lands were dominated by a noble class known as the boyars, above whom stood the grand prince and later the tsar, an absolute monarch. The groundwork of the Russian Empire was laid by Ivan III (r. 1462–1505), who greatly expanded his domain, established a centralized Russian national state, and secured independence from the Tatars. His grandson, Ivan IV (r. 1533–1584), became in 1547 the first Russian monarch to be crowned tsar of all Russia. Between 1550 and 1700, the Russian state grew by an average of 35,000 km2 (14,000 sq mi) per year. Peter I transformed the tsardom into an empire, and fought numerous wars that turned a vast realm into a major European power. He moved the Russian capital from Moscow to the new model city of Saint Petersburg, and led a cultural revolution that introduced a modern, scientific, rationalist, and Western-oriented system. Catherine the Great (r. 1762–1796) presided over further expansion of the Russian state by conquest, colonization, and diplomacy, while continuing Peter's policy of modernization. Alexander I (r. 1801–1825) helped defeat the militaristic ambitions of Napoleon and subsequently constituted the Holy Alliance, which aimed to restrain the rise of secularism and liberalism across Europe. Russia further expanded to the west, south, and east, strengthening its position as a European power. Its victories in the Russo-Turkish Wars were later checked by defeat in the Crimean War (1853–1856), leading to a period of reform and conquests in Central Asia. Alexander II (r. 1855–1881) initiated numerous reforms, most notably the 1861 emancipation of all 23 million serfs.

By the start of the 19th century, Russian territory extended from the Arctic Ocean in the north to the Black Sea in the south, and from the Baltic Sea in the west to Alaska, Hawaii, and California in the east. By the end of the 19th century, Russia had expanded its control over the Caucasus, most of Central Asia and parts of Northeast Asia. Notwithstanding its extensive territorial gains and great power status, the entered the 20th century in a perilous state. The devastating Russian famine of 1891–1892 killed hundreds of thousands and led to popular discontent. As the last remaining absolute monarchy in Europe, the empire saw rapid political radicalization and the growing popularity of revolutionary ideas such as communism. After the Russian of 1905, the last emperor, Nicholas II (r. 1894–1917), authorized the creation of a national parliament, the State Duma, though ultimate political authority remained with him.