Gamma rays, also known as gamma radiation, is a penetrating form of electromagnetic radiation that is emitted from the radioactive decay of atomic nuclei. For imparting the highest photon energy, it consists of the shortest wavelength electromagnetic waves. To understand and identify the decaying radionuclides, the use of gamma spectroscopy is essential. Radioactive decay, terrestrial thunderstorms, solar flares, cosmic rays, pulsars and magnetars, and quasars are some of its main sources. Gamma rays that originate on earth are typically a result of radioactive decay and secondary radiation from the atmospheric interaction of cosmic ray particles. This book elucidates new techniques of gamma rays, current trends and future prospects in a multidisciplinary manner. It strives to provide a fair idea about this discipline and to help develop a better understanding of the latest advances within this field. Coherent flow of topics, student-friendly language and extensive use of examples make this book an invaluable source of knowledge.