Wireless and self-powered systems for consumer electronics have been in a rising trend in recent years as a result of developments in alternative energy studies, unsustainable nature of fossil fuels, and environmental concerns. In this context, among alternative energy sources, piezoelectric, triboelectric, thermoelectric, pyroelectric, and electromagnetic conversion are the main mechanisms for energy generation in large and/or small scale applications. Piezoelectric devices are one of the most attractive systems among these for energy and sensing applications. Piezoelectric material-based mechanical, vibration, wind, sound, and even biomechanical energy harvesters have been produced by many researchers. In this section, the concept of piezoelectricity, piezoelectric energy harvesting theory, piezoelectric materials, and energy applications based on piezoelectric materials will be discussed.