Radio frequency power measurement has been an important component of semiconductor processing since the time that plasma was first used for wafer processing. Power measurement was, and continues to be important, as radio frequency energy is used to excite the plasma, and the plasma characteristics are in large part determined by the excitation energy. In this article, we will discuss various means of measuring radio frequency power, along with their limitations. In addition, we will present the best calibration methods for radio frequency power measuring instruments.