This book is an introduction to radioactivity and aerosols for the scientifically literate reader with little or no previous exposure to either of these subjects. It provides a step-by-step introduction to radioactive aerosols from the physical science perspective, with coverage of such topics as indoor radon decay products, radioactive aerosols as tracers of atmospheric processes, indoor and outdoor models of aerosol transport, fallout from nuclear weapons and reactor accidents, and measurement of radioactivity and aerosols. Audience: Although it includes references to the research literature, it is not designed as a research monograph for specialists. Rather, it is directed at an interdisciplinary audience at the advanced undergraduate science level and higher who want an introductory, but rigorous, presentation of the core material of this subject. It is suitable for self study or for use as a main or supplemental textbook. It should be useful to a range of students in aerosol science, health physics, environmental science, nuclear engineering, and the atmospheric sciences. It should also be valuable to 'crossover' professionals - professionals in other areas of science and engineering - who want a readable, self-contained introduction to radioactive aerosols. Many worked examples, and more than a hundred exercises and problems with answers, are provided.