Piezoelectric energy harvesting technologies have received a great attention during the last decade to design self-powered microelectronic devices such as wireless sensor nodes (WSN). Piezoelectric energy harvester (PEH) produces maximum power when its natural frequency closely matches the excitation vibration frequency. In most of real-time applications, frequency of the vibration source is not constant but it is time-varying. Hence, the piezoelectric energy harvester has to be “self tunable” in order to guarantee that its natural frequency closely matches with the excitation frequency. Different tuning methods are surveyed and analyzed intensively in this book. A lumped dynamic model for a piezoelectric cantilever is developed using parametric identification to simply build up the equivalent circuit. Power analysis for the energy harvester is developed to investigate the necessary conditions for the maximum power transfer. A self-tunable piezoelectric energy harvester using servo motor represents the main contribution in this book. The system performance is enhanced where the frequency bandwidth is increased.