This book presents recent research in the field of piezoelectric vibration energy harvesting in which intentionally designed nonlinearities as well as inherently present are widely considered. It provides an overview of the state-of-the-art, with a sharp classification into linear and nonlinear devices, and recalls the fundamentals of piezoelectricity and magnetostatics. A detailed treatment of linear and nonlinear mathematical modeling of piezoelectric harvesters is then developed to provide the reader with a wide range of modeling possibilities. Theoretical, computational, and experimental approaches to modeling the magnetic interaction are also provided. Several cases of innovative piezoelectric harvester designs based on magnetic interaction as a frequency up-conversion mechanism (FuC) are developed. Improvements of the magnetic FuC are proposed, in combination with indirect impacts as well as the manipulation of magnetic forces with novelty methods. Novel studies on the magnetic interaction itself and its implications for the dynamic behavior of the harvester are also summarized. The book provides an integrated view of theoretical, computational, and experimental research in this field, as such it can be useful for researchers interested in linear and nonlinear piezoelectric energy harvesting, for graduate courses on smart structures and devices, microsystems, and for designers.