The basic goal of this book is to examine the complex state of radioactivity in the environment, including its sources and applications. In principle, there are two sources of environmental radioactivity, namely man-made and natural. The authors of this book set out to analyze mainly empirical aspects of the activities of both groups. On one hand, a detailed analysis of the sources releasing radionuclides into the environment by human activities should, while describing environmental pollution and its dangers, contribute to its decrease in the future. On the other hand, the analyses of natural radionuclides, as well as their influences and use in different fields, serve to complete an evaluation of the present state of environmental radioactivity. All auxiliary parts (e.g., principles of radionuclide analyses) are included to the extent necessary for understanding the basic themes. The many recent examples contained in the book will be useful in studying various problems of radioactivity in the present environment, and can help, not only in preparing, carrying out and evaluating outdoor and laboratory experiments, but also in protection of the environment and human health through a