Even though the analytical aspects of the torsional response of a rotor system are straightforward, actually measuring the torsional response has been historically very difficult and therefore somewhat neglected. It is recognized that dynamic torsional stresses can contribute significantly to the total operating stresses imposed on a rotor system in rotating machinery, as there are many reports of serious or catastrophic rotor system damage caused by high torsional stress. Thus, measuring and continuously monitoring the torsional dynamic stresses in an operating environment is fundamentally important to assure that a rotor system is operating for its intended application and to assure that impact is insignificant with any operational changes. With a brief review of torsional response analytical principles, this paper focuses on the interpretations of the torsional measurements along with the available methods for measuring and implementing the measurement results for rotating component life assessment. Also, a critique of the available methods for measuring and for monitoring rotor system torsional dynamic response in the actual operating environment is provided. In addition, the paper provides a highlight of a recently developed sensor technology. All efforts serve the purpose to re-emphasize the importance of monitoring rotor torsional response to the industry.