This book is intended for use in a first course on the physics of the atomic nucleus and is based on lectures given in the 'core' course to students of physics at the University of Bristol. The authors' aim is to provide a clear and comprehensive account of the basic concepts. The text opens by setting nuclear physics in the context of elementary particle physics. The authors then show how the application of simple models can provide an understanding of the properties of nuclei, both in their ground states and excited states, and also of the nature of nuclear reactions. The book includes chapters on nuclear fission and its application in nuclear power reactors, and on the role of nuclear physics in energy production and nucleosynthesis in stars. The authors assume a knowledge of basic quantum mechanics and special relativity, but there are appendices on some other more specialized but relevant topics. Each chapter ends with a set of problems applying and extending the material covered in the text. This book will fill the need for a concise introduction to one of the most fundamental subjects taught to undergraduates in physics.