This thoroughly revised book, now in its third edition, continues to provide a comprehensive introduction to this increasingly important area of nuclear and particle physics. It combines coverage of basic concepts, principles and applications, along with the latest developments. Beginning with the historical developments of the subject, properties and constituents of the nucleus, quantitative facts about nucleus, etc., the book moves on to give insights into nuclear models, phenomenon of radioactivity and its applications in various fields, nuclear reactions including reactions in sun and stars, photoelectric and Compton effects, pair production, particle accelerators and types of radiation detectors. The text also presents an extensive discussion on elementary particles and their fundamental reactions, fundamental forces, conservation laws and the quark model. Besides updating and revising the existing text, the new edition amplifies several sections across the book for easy understanding of the topics discussed.