This document discusses piezoelectric energy harvesting. It begins with an introduction to piezoelectricity and describes the direct and converse piezoelectric effects. It then explains that piezoelectric energy harvesting is a type of micro-scale energy harvesting that uses vibrations as an input source. Examples of vibration sources are given as well as a basic block diagram of a piezoelectric energy harvesting circuit. Applications are listed along with advantages such as being pollution-free and unaffected by magnetic fields and disadvantages such as crystals being vulnerable to overstress or high temperatures.