This is an up-to-date textbook for biologists and biomedical scientists covering the basics of radioisotope methodology and safety. Radioisotopes are widely used in biological and medical research, particularly in biochemistry. Graduate students and technicians usually learn how to use radioisotopes through short training courses or as part of laboratory courses in biology and biochemistry. This text was written for use in courses on the theoretical aspects of radioisotopic methods or for self-study and reference; it assumes little knowledge of radioactive materials and develops mathematical discussions slowly and clearly.