This book provides a thorough yet concise introduction to quantitative radiobiology and radiation physics, particularly the practical and medical application. From basic science to contemporary applications--the definitive guide to radiobiology theory and practice This book is based on courses taught over many years to individuals preparing for certification or registry examinations to demonstrate their knowledge of radiation and its effects. We also taught CME courses to practicing physicians required to demonstrate their maintained level of competence in radiology and cardiology. Engineers, scientists, and radiation safety specialists also attended many of these courses. Through teaching these classes, we observed that most of our students didn't know or remember much about physics or biology. Practicing physicians and medical professionals were far from current in their knowledge of radiation and its biological effects. We felt a need for a book for the "users" of radiation which would include sections for reviewing basic physics and biology. The authors are a team of scientists and engineers with over a century of combined experience teaching and working with radiation and biology. We are "users" of radiation and mindful of its effects. The first quarter of the book is designed to ensure the reader has a minimum essential knowledge base in biology and physics. The book then covers DNA structure and function, DNA damage and repair, genetic effects, and the characteristics of cancer. The third quarter of the book covers the effects of radiation on various body organs and the entire body as well as effects remote from the site of radiation (the bystander effect). A discussion of the cumulative effect of many small doses of radiation is included. The differences between radiation doses in diagnostic, therapeutic, and nuclear medicine are thoroughly discussed. The last quarter includes chapters describing the effects from medical and natural sources of radiation, while also incorporating a discussion of how regulations are designed to protect workers and the general public from long-term harmful effects. Chapters on the biological effects of MRI and ultrasound are included to complete the book's coverage, although the radiation from an MRI or ultrasound does not produce ionization. Each chapter contains a clear statement of the chapter goals, an extensive body of material with figures and illustrations, and a summary of the important points covered in the chapter. Each chapter concludes with a series of multiple choice questions in the style and level of difficulty of many national examinations.