Nowadays, ‘green’ communication is of great importance to save electric energy. In communication systems, power amplifiers (PAs) play an important role and consume large amount of power. As a consequence, the enhancement of amplifier efficiency is significantly important for saving energy.   This thesis describes a method to enhance the amplifier efficiency. The goal for this thesis is to find the matching impedances of harmonics for optimum efficiency performance of an amplifier. The idea is to control and change the load impedances at 2nd and 3rd harmonics for maximum efficiency performance of an amplifier at fundamental frequency and finally to build a matching network according to the matching impedances at harmonics.   The load pull technique is applied in this thesis to control the impedances with automatically controlled tuners. In this way, different impedances correspond to specific tuner positions. Then for different tuner positions, the corresponding load impedances of the harmonics are determined, the input, output as well as DC power of the amplifier are measured, and the corresponding efficiency is computed. Therefore, after appropriate efficiency sweep for specific tuner positions, the matching impedances with maximum efficiency performance can be found.   The efficiency of the amplifier with harmonic matching (the method implemented in this thesis) can be improved 2.13 percent which proves the feasibility of the method investigated in this thesis.