Vibrational energy harvesting spans both new technology and traditional technology space. The latter is represented well by wind up watches and the former by self-powered autonomous sensor networks, which is the subject of intense academic and industrial research and development. In this study, the authors introduce the concepts of vibrational energy harvesting with an emphasis on piezoelectric technology. However, much can be learned from more traditional transduction technologies such as electromagnetic so they also discuss some of these systems. The transfer of vibrational energy from its mechanical domain to a useful electrical domain is complex and in this section they explore ways in which the electrical charge (electrical energy state) can be efficiently rectified from its AC character to a viable DC voltage for storage or immediate loading. Finally, they examine some of the very new technologies which permit harvesting of vibrational energy on the very small scale using micro-electromechanical systems based technologies. This length scale is important and better matches the energy density of small scale vibrational sources and power output densities of piezoelectric materials in particular.