In February and March 2014, Russia invaded the Crimean Peninsula, part of Ukraine, and then annexed it. This took place in the relative power vacuum immediately following the Revolution of Dignity. It marked the beginning of the Russo-Ukrainian War.

The events in Kyiv that ousted Ukrainian president Viktor Yanukovych on 22 February 2014 sparked both pro-Russian and anti-separatism demonstrations in Crimea. At the same time, Russian president Vladimir Putin told his security chiefs to begin work on "returning Crimea to Russia". On 27 February, Russian special forces without insignia seized strategic sites across Crimea. Russia at first denied involvement, but Putin later admitted that they were Russian troops. As the armed men occupied Crimea's parliament, it dismissed the Crimean government, installed the pro-Russian Aksyonov government, and announced a referendum on Crimea's status. The referendum was held under Russian occupation and, according to the Russian-installed authorities, the result was overwhelmingly in favor of joining Russia. The next day, 17 March 2014, Crimea's authorities declared independence and requested to join Russia. Russia formally incorporated Crimea on 18 March 2014 as the Republic of Crimea and federal city of Sevastopol. Following the annexation, Russia militarized the peninsula and warned against any outside intervention.

Ukraine and many other countries condemned the annexation and consider it to be a violation of international law and Russian agreements safeguarding the territorial integrity of Ukraine. The annexation led to the other members of the G8 suspending Russia from the group and introducing sanctions. The United Nations General Assembly also rejected the referendum and annexation, adopting a resolution affirming the "territorial integrity of Ukraine within its internationally recognised borders", and referring to the Russian action as a "temporary occupation".

The Russian government opposes the "annexation" label, with Putin defending the referendum as complying with the principle of the self-determination of peoples.

The names of the Crimean annexation vary. In Ukraine, the annexation is known as the temporary occupation of the Autonomous Republic of Crimea and Sevastopol by Russia (Ukrainian: тимчасова окупація Автономної Республіки Крим і Севастополя Росією, romanized: tymchasova okupatsiia Avtonomnoi Respubliky Krym i Sevastopolia Rosiieiu), the illegal occupation of the Autonomous Republic of Crimea, the fall of Crimea, and the invasion of Crimea.

In the Russian Federation, it is also known as the accession of Crimea to the Russian Federation (Russian: присоединение Крыма к Российской Федерации, romanized: prisoyedineniye Kryma k Rossiyskoy Federatsii), the return of Crimea (Russian: возвращение Крыма, romanized: vozvrashcheniye Kryma), and the reunification of Crimea.

Crimea was part of the Crimean Khanate from 1441 until it was annexed by the Russian Empire in 1783 by a decree of Catherine the Great.

After the downfall of Russian empire in 1917 during the first stages of the Russian Civil War there were a series of short-lived independent governments (Crimean People's Republic, Crimean Regional Government, Crimean SSR). They were followed by White Russian governments (General Command of the Armed Forces of South Russia and later South Russian Government).