The Nizari state was a Nizari Isma'ili Shia state founded by Hassan-i Sabbah after he took control of the Alamut Castle in 1090 AD, which marked the beginning of an era of Ismailism known as the "Alamut period". Their people were also known as the Assassins or Hashashins.

The Nizaris are the largest segment of the Ismaili Muslims, who are the second-largest branch of Shia Islam after the Twelvers. Nizari teachings emphasize independent reasoning or ijtihad; pluralism—the acceptance of racial, ethnic, cultural and inter-religious differences; and social justice. Nizaris, along with Twelvers, adhere to the Jaʽfari school of jurisprudence. The Aga Khan, currently Aga Khan IV, is the spiritual leader and Imam of the Nizaris. The global seat of the Ismaili Imamate is in Lisbon, Portugal.