Radioisotopes have found wide use in chemistry because of their distinctive qualities. The case with which a radioisotope is detected and the precision, with which it can be measured, even in minute quantities, leads to not only its use as analytical tool of great versatility but the phenomenon like co-precipitation, solvent extraction, chromatographic and ion exchange methods, surface absorption, mechanism of inorganic and organic reactions, structural confirmations, all can be investigated. At present there are up to 200 radioisotopes used on a regular basis, and most must be produced artificially. There are several books available written by persons of international fame in this field. This presentation has emerged from the author's lectures given during various physical chemistry courses in the last many years and presented in a simple way so that the students would be better equipped for mastering any advanced level course in the field of Radiochemistry and Nuclear Chemistry. This book covers the following topics: Nuclear decay, Radioisotopes, Kinetics of decay, Radioactive measurements, Statistics, Chemical effects, Mossbauer spectroscopy, Chemical applications, and Hazards.