Abu Ali Hasan ibn Ali Tusi (April 10, 1018 – October 14, 1092), better known by his honorific title of Nizam al-Mulk (Persian: نظام‌الملک, lit. 'Order of the Realm') was a Persian scholar, jurist, political philosopher and Vizier of the Seljuk Empire. Rising from a lowly position within the empire, he effectively became the de facto ruler of the empire for 20 years after the assassination of Sultan Alp Arslan in 1072, serving as the archetypal "good vizier". Viewed by many historians as "the most important statesman in Islamic history", the policies implemented by Nizam al-Mulk would go on to remain as the basic foundation for administrative state structures in the Muslim world up until the 20th Century.

One of his most important legacies was the founding of the madrasa system in cities across the Seljuk Empire which were called the Nizamiyyas after him. This was seen to be as the first government sponsored education system in history and as the inspiration behind the university system in Western Europe. He also wrote the Book of Government, a political treatise that uses historical examples to discuss justice, effective rule, and the role of government in Islamic society, which would go on to inspire the works of Ibn Khaldun and became the prototype for Machiavellian thought throughout Europe.