Pi Tau Sigma (ΠΤΣ) is an international honor society in the field of mechanical engineering.

Pi Tau Sigma was established on March 16, 1915, at the University of Illinois.

[2] Pi Tau Sigma was formed as a national honor society for men in the field of mechanical engineering.

[3] Pi Tau Sigma's key features the Carnot cycle.

[3][1] Upperclassmen and graduate students studying mechanical engineering are eligible to join Pi Tau Sigma, based on academic performance.