Discussed is the thermomechanical fatigue (TMF) life of Type 316 stainless steel under in-phase and out-of-phase cycling and a comparison with the isothermal fatigue case. The TMF tests were conducted in air over a temperature range of 399‡C (750‡F) to 621‡C (1150‡F) at several mechanical strain ranges: δε^m = 0.4% through 1.0%. The isothermal fatigue data were from total strain range (δε^m = 0.35%, 0.5%, 0.68% and 1.0%) tests conducted at 621‡C (1150‡ F). The results show that in-phase TMF is the most damaging cycle for Type 316 stainless steel at the high strain range levels (δε^m > 0.7%), followed by isothermal fatigue cycling at 621‡C (1150‡F) and then out-of-phase TMF cycling. The out-of-phase TMF life curve was observed to cross over the isothermal fatigue life curve at δε^m ≅ 0.6%, and the trend of the data indicate that the out-of-phase TMF life curve will cross over the in-phase TMF life curve at δε^m < 0.4%, and become the most damaging cycle type at the lower strain range levels.