Siger of Brabant (Sigerus, Sighier, Sigieri or Sygerius de Brabantia; c. 1240 – before 10 November 1284) was a 13th-century philosopher from the southern Low Countries who was an important proponent of Averroism. He was considered a radical by the conservative members of the Roman Catholic Church, but it is suggested that he played as important a role as his contemporary Thomas Aquinas in the shaping of Western attitudes towards faith and reason.
Little is known about many of the details of his life. In 1266, he was attached to the Faculty of Arts in the University of Paris at the time when a riot erupted between the French and Picard "nations" of students—a series of loosely organized fraternities. The papal legate threatened Siger with execution as the ringleader of the Picard attack on the French, but no further action was taken.
In the ten years following the riot, he wrote the six works which are ascribed to him and were published under his name by Pierre Mandonnet in 1899. The titles of these treatises are: