Triangle is a fraternity for male students majoring in engineering, architecture, and the physical, mathematical, biological, and computer sciences. It is the only member of the North American Interfraternity Conference to limit its membership recruitment to these majors.

Triangle Fraternity organized at the University of Illinois at Urbana–Champaign in the fall of 1906 and was incorporated by the state of Illinois on 15 April 1907, which is celebrated each year as Founders' Day.

As of February 2020 there are thirty-nine chapters and six colonies of Triangle Fraternity active in the U.S. The headquarters is located in Plainfield, Indiana in a historic building erected as a Carnegie library in 1912.Triangle Fraternity is one of three active national fraternities not to use Greek letters for its name, the others being Acacia and FarmHouse.