In this chapter, the different alternative and mixed-mode configurations of high-efficiency power amplifiers are presented. A Class-DE power amplifier is based on the combination of a voltage-switching Class-D mode with Class-E switching conditions, thus extending the switching Class-D operation to higher frequencies. Effects of the saturation resistance and nonlinear capacitance, driving waveforms, and some practical examples of Class-DE power amplifiers are discussed. The switched-mode Class-E/F power amplifier can provide lower voltage peak factors when zero voltage and zero voltage-derivative conditions corresponding to Class-E mode, required to eliminate discharge loss of the shunt capacitance, are accompanied by harmonic tuning using the resonant circuits tuned to selected harmonic components realizing Class-F mode. Also, the biharmonic Class-E _M mode is described, which can eliminate the efficiency degradation of a Class-E operation mode at higher frequencies due to the increased switching power losses with increasing values of the turn-off switching time. The requirements of both jumpless voltage and current waveforms and sinusoidal load waveform with nonzero output power delivered to the load can be provided by using nonlinear reactive elements in the load network to convert fundamental-frequency power to a desired harmonic frequency or by injecting the harmonic-frequency power into the load network from an external source. An inverse Class-E power amplifier represents an inverse version of a classical Class-E power amplifier with a shunt capacitor where the load network inductor and capacitor replace each other. Generally, it is limited to low operating frequencies or low output powers since it is based on...