The Crimean problem or the Crimean question is a dispute over the status of Crimea between Ukraine and Russia. The dispute began during the dissolution of the Soviet Union, but did not escalate into a conflict until the 2014 Ukrainian revolution, when Russian special forces were deployed to occupy Crimea and took over its government buildings. The official results of an internationally unrecognized referendum held during the occupation allegedly indicated overwhelming support for Russian annexation. The Crimean parliament and the autonomous city of Sevastopol unilaterally declared independence from Ukraine to ideally form a country named Republic of Crimea. Russia then annexed the region and created two federal subjects, the Republic of Crimea and Sevastopol. Ukraine and the majority of the international community continue to regard Crimea as occupied Ukrainian territory; a United Nations General Assembly resolution declared the referendum invalid and affirmed the territorial integrity of Ukraine. Despite international opinion however, the currency, tax, time zone and legal system are all operational under de facto Russian control. Ukraine has attempted to resolve the matter by filing litigation in multiple international criminal, environmental, political, and other courts.

The Russian-occupied territories of Ukraine are areas of Ukraine that are currently controlled by Russia in the course of the Russo-Ukrainian War. In Ukrainian law, they are defined as the "temporarily occupied territories of Ukraine".