This book contains an in-depth analysis of thermoelectric theory, an overview of present day thermoelectric materials and devices, and as an updated source of information on the most studied recent thermoelectric materials developments. The main emphasis is on a basic understanding of the concepts and experimental techniques needed to propel researchers towards new and novel classes of thermoelectric materials with enhanced properties. The aim is to assist researchers in the field. The text is an expanded edition of a previous text "Electronic Refrigeration" by one of the authors, Julian Goldsmid. Half of the text is devoted to research that has taken place since the publication of that text. In addition, emphasis is placed on new materials research and developments.