The Pi Sigma Fraternity is a national fraternity which is committed to the principles of Paglingkuran ang Sambayanan and Paragon of Scholarship. Forged at the height of the martial law period, specifically on 15 August 1972, in University of the Philippines in Diliman, the fraternity seeks to contribute to the Filipino people's struggle for a free, just and humane society as well as to carve a fraternity system that is not macho-oriented and rumble-prone.

From its lone chapter in the University of the Philippines (UP) in Diliman, the Pi Sigma Fraternity has since established chapters nationwide, in almost all UP units, i.e. UP Manila, UP Los Banos, UP San Fernando, and UP Baguio. Its membership is spread out in more than a hundred school and community chapters in Northern Luzon, Central Luzon, Metro Manila, Southern Luzon, and Mindanao.