Nanogenerators are an emerging technology, a novel provider of renewable energy in a range of applications, such as energy harvesters and self-powered sensors. Understanding how physical phenomena can be converted into electricity is key to the design of energy harvesters and sensors and their future applications. With a focus on mechanical and biomechanical energy, this book introduces the physical principles of piezoelectricity and triboelectricity and directs the reader to the materials and fabrication methods available. The pros and cons of both are considered, and a further chapter explores hybrid and alternative systems. In taking this approach the author presents the most essential information on nanogenerators. Applications provide a practical context and the book concludes with the author's views on the future. References to the literature throughout guide the reader to explore this exciting topic further.