Nuclear Science is the study of the Components, Structure and Behaviour of the Nucleus of an Atom. It is especially concerned with the nature of matter and with nuclear energy. Nuclear physicists investigate nuclear matter on all scales, from sub-atomic particles to supernovas. Research areas include the structure of the nucleus at different temperatures and pressures, the origin of elements and the structure and evolution of stars. The contribution of Nuclear Science to Energy Sector, Medical Sciences, Biology, and Radiobiology and too many other fields is now well recognised. The widespread applications of nuclear techniques and their strong impact on society require an education of the general public in the concept of elementary nuclear phenomena. Encyclopaedia of Nuclear Science is written from an experimental point of view, it discusses the fundamental concepts and practical applications of Nuclear Science in detail. Its Chapters include Nuclear Science, Nuclear Structure, Atomic Nucleus, Composite Structure of an Atom, Ionizing Radiation, Nuclear Technology, Radiography, Radiation Therapy, Features of Radioactivity, X-Ray, Application of MRI, Artificial Fusion, Fission of Heavy Elements, Fusion Power, Systems of Nuclear Instrumentation, and Nuclear Power Reactors. This Encyclopaedia is based on Syllabus provided by Indian Universities and it is hoped that the present Encyclopaedia will be highly useful for students and teachers.