This book provides a coherent and comprehensive overview of the generation and application of mono-energetic positron beams. It has been written by acknowledged experts, at a level accessible to graduate students working, or planning to work, with positron beams, and to scientists in other areas who want to know something about the field.The book begins with a brief historical introduction and an overview of how positron beams are generated and transported. A description of the fate of slow positrons in gaseous and condensed matter, with reference to many of the fundamental measurements made possible by the advent of positron beams, is followed by a discussion on applications in the study of solid surfaces, defect profiling in subsurface regions, interfaces and thin films, and the probing of bulk properties in novel ways. The book ends with a look at the future, considering the prospects for intense positron beams and their potential for further research.