The Crimean War (pronounced /kraɪˈmiːən/ or /krɨˈmiːən/) (October 1853 – February 1856) was a conflict between the Russian Empire and an alliance of the French Empire, the British Empire, the Ottoman Empire, and the Kingdom of Sardinia. The war was part of a long-running contest between the major European powers for influence over territories of the declining Ottoman Empire. Most of the conflict took place on the Crimean Peninsula, but there were smaller campaigns in western Anatolia, Caucasus, the Baltic Sea, the Pacific Ocean and the White Sea. In Russia, this war is also known as the "Eastern War" (Russian: Восточная война, Vostochnaya Voina), and in Britain it was also called the "Russian War" at the time.

The Crimean War is known for the logistical and tactical errors during the land campaign on both sides (the naval side saw a successful Allied campaign which eliminated most of the ships of the Russian Navy in the Black Sea). Nonetheless, it is sometimes considered to be one of the first "modern" wars as it "introduced technical changes which affected the future course of warfare," including the first tactical use of railways and the electric telegraph. It is also famous for the work of Florence Nightingale and Mary Seacole, who pioneered modern nursing practices while caring for wounded British soldiers.