The introduction and formulation of the "Continuous" modes of transistor operation has provided an alternative design route for the realization of high efficiency power amplifiers (PA's) over a wide bandwidth (approaching an octave). The formulation of the "Continuous" modes provides a mathematical framework for extending the fundamental/harmonic impedance space over which the power and efficiency performance of the traditional PA modes, i.e. Class, B, Class F, etc, can be maintained. This mathematical framework has been experimentally validated using RF I-V waveform engineering measurements systems and the realization of demonstrator PA prototypes.Index Terms -Microwave measurements, microwave theory and techniques, power amplifiers, power transistors, wideband.