Alamut (Persian: ?????; transliterated Alamut) was a mountain fortress located in the South Caspian province of Daylam near the Rudbar region in Iran; approximately 100 kilometres (60 mi) from present-day Tehran; Iran. The name means 'Eagle's Nest'.

Under the leadership of Hasan-i Sabbah; Alamut became the site of intense activity for the Shi'a Nizari Ismaili Muslims; along with a smaller subgroup known as the Assassins; between 1090 and 1256 AD. During the medieval period; the castle functioned as the major stronghold of the Nizari Ismaili state. In 1256; Ismaili control of the fortress was lost to the invading Mongols and its famous library holdings were destroyed when the castle's library was condemned to be burned by 鈥楢ta-Malik Juwayni; a servant of the Mongol court. Sources on the history and thought of the Ismailis in this period are therefore lacking and the majority extant are written by their detractors.

After the Mongol destruction; the castle was of only regional significance; passing through the hands of various local powers. Today; it lies in ruins; but because of its historical significance; it is being developed by the Iranian government as a tourist destination.