Theta Tau (ΘΤ) is a professional collegiate engineering fraternity. The fraternity has programs to promote the social, academic, and professional development of its members. Theta Tau is the oldest and largest professional engineering fraternity and has a membership of more than 50,000 men and women who study engineering in all its various branches on over 100 college campuses.

The Theta Tau Central Office is located in Springfield, Missouri.

Theta Tau was founded by four engineering students at the University of Minnesota in Minneapolis, Minnesota as the Society of Hammer and Tongs on October 15, 1904. Its founders were Erich J. Schrader, Elwin L. Vinal, William M. Lewis, and Isaac B. Hanks, who were all mining engineering students. They agreed that character qualification should have top priority in membership selection.

Schrader served as its first Grand Regent and was chiefly responsible for the ritual, constitution, and bylaws adopted by the founders. He created one of the original artifacts of incorporation for the Society of Hammer and Tongs, the bolt of "strength and unity" in late 1904.

The constitution provided for the establishment of additional chapters at other leading engineering schools, and the fraternity soon began to expand nationally. Hanks spoke of the fraternity to his friend, Robert Downing, a member of the Rhombohedron Club at Michigan College of Mines. After correspondence and an inspection trip by Hanks, the club was installed as Beta chapter in 1906. Lewis transferred to the Colorado School of Mines and contacted the Square Set Club, which became the Gamma chapter in 1907. The Southwestern Alumni Association, the fraternity's first, was established in Douglas, Arizona, in 1908.

In 1911, representatives of the three chapters and the alumni association met at the University of Minnesota for the first national convention. The name was changed to Theta Tau, a revised ritual was approved, and the present badge was adopted. Perhaps most important for its future expansion, they decided that Theta Tau would include all branches of engineering.

In the next two years, Delta, Epsilon, Zeta, and Eta chapters were installed. The second convention was held in Houghton, Michigan, in 1913. That convention designated The Gear of Theta Tau as the national fraternity's magazine and appointed Jack E. Haynes, A '08, as its first editor-in-chief. Previously, the magazine had been published by Beta chapter with Herman H. Hopkins, B '08, as editor. Hopkins, a member of the Rhombohedron Club, had been initiated by Beta chapter as an alumnus. He served until 1919 as the Grand Scribe and later (1935) was elected Grand Regent.

The third (1915) and fourth (1919) conventions were held in Cleveland, Ohio. Meanwhile, Theta, Iota, and Kappa chapters were installed. Elected as Grand Regent in 1919 was Dr. George D. Louderback, E '96, a charter member of the Epsilon chapter. During his tenure, rapid growth continued, with nine more chapters being installed. In 1920, Schrader became the Grand Scribe, serving in this capacity for 35 years.