This document discusses piezoelectricity and its applications for energy harvesting. It begins by introducing piezoelectricity and some common natural and synthetic piezoelectric materials. It then describes how piezoelectric materials work and can be used in transducers. Examples are given of harvesting energy from human footsteps on sidewalks or in dance clubs, and from vibrations in vehicles, mobile devices, and gyms. The output power from individual crystals is small but can be increased by combining crystals. Other applications mentioned include cigarette lighters and sensors. Advantages are listed as being pollution-free and having low maintenance, while disadvantages include low power output and susceptibility to cracking.