The siege of Samarkand (1220) took place in 1220 A.D. after Genghis Khan, founder of the Mongol Empire, had launched a multi-pronged invasion of the Khwarazmian Empire, ruled by Shah Muhammad II. The Mongols had laid siege to the border town of Otrar, but finding its defences obdurate, a large force commanded by Genghis and his youngest son Tolui detached from the vanguard and set off southwards, towards Transoxiana.

Genghis Khan, also Chinggis Khan, was the founder and first khan of the Mongol Empire, which he ruled from 1206 until his death in 1227; it later became the largest contiguous empire in history. After spending most of his life uniting the Mongol tribes, he launched a series of military campaigns, conquering large parts of China and Central Asia.