Nuclear physics is the study of the nuclei of atoms and their interactions. This textbook is a comprehensive, balanced, and up to date introduction to the subject. It describes both the experiments made to study nuclear reactions and nuclear structure, and the theories and models that have been developed to understand the properties of nuclei and their interactions. Introductory nuclear physics will serve both as a textbook for undergraduates and graduates, and as a useful reference work for professional nuclear physicists.