In the last decades the increasing need to produce energy in nontraditional ways has led to researchers searching for cheap and environmentally safe sources of energy. This has caused a growing interest in Energy Harvesting, which is a science that tries to capture energy provided by wind, rain, or other natural vibrations to convert it into a different more useful form of energy. The first chapter of this book studies a model which simulates a 'small' cantilever beam, and evaluates the optimal thickness for the cantilever, comparing the reaction to wind force of difference devices with the same shape but different thickness of piezoelectric layer. Chapter two discusses three energy conversion schemes with special emphasis placed on micro electret-based electrostatic energy conversion mechanisms. Chapter three studies modeling on piezoelectric energy harvesting from pavements under traffic control. Chapter four investigates the Aero/hyrdro elastic phenomena such as Fluttering, Galloping, Buffering, and Vortex Induced Vibration for energy harvesting. Chapter five introduces the concept of energy harvesting from water systems, and the established technologies and projects under development to recover energy from water networks are presented. Chapter six examines a piezoelectric power supplier for underwater applications, which is optimised to feed magnetic sensors. The final chapter describes a novel power generation from algae based on the combination of exergy recovery and process integration technologies.