This book is intended as an introduction to radioactivity and aerosols for the scientifically literate reader who has had no previous exposure to either of these subjects. Although its main focus is radioactive aerosols, on the road to this subject I provide short, somewhat independent introductions to both radioactivity and aerosols, with some emphasis on experimental aspects. The audience I have in mind is upper-level undergraduates or beginning graduate students with a minimum background of introductory college courses in physics, chemistry, and calculus. This book may also be useful to "crossover" professional- professionals in other fields of science and engineering, for example biology or geoscience, who would like a step-by-step introduction to this subject matter from the physical science perspective. In writing this book I have been sensitive to requests and suggestions from students who need some background in this subject matter but will probably not specialize in it. These students are bright, but busy, and they sometimes feel overwhelmed by the mass of information in advanced, comprehensive texts. No matter how noble the intentions of the authors (or the teachers assigning the books!), these students often do not have time to read such books through cover to cover, and they fmd it difficult to pick out a coherently-connected subset of the material. Furthermore, modern students studying an interdisciplinary subject like radioactive aerosols are likely to be more diversified than ever, in educational background, in interests, and in preparation.