A new edition of a book is warranted when the book is successful and there are many new developments in the related discipline. Both have occurred for this book during the past 7 years since its second edition. The growth and development in nuclear pharmacy and radiopharmaceutical chemistry along with the continued success of the book have convinced us to update the book; hence this third edition. This book is a ramification of my nuclear pharmacy courses offered to pharmacy students specializing in nuclear pharmacy, nuclear medicine resi dents, and nuclear medicine technology students. The book is written in an integrated form from the basic concept of atomic structure to the practical clinical uses of radiopharmaceuticals. It serves both as a textbook on nu clear pharmacy for pharmacy students and nuclear medicine technologists, and as a useful reference book for many professionals related to nuclear medicine, such as nuclear medicine physicians and radiologists. The book contains 12 chapters. Each chapter is written as comprehen sively as possible based on my personal experience and understanding. At the end of each chapter, a section of pertinent questions and problems and so me suggested reading materials are included. I have made justifiably many additions and deletions as weIl as some reorganization in this edition. Chapter 3 is entirely dedicated to instru ments for radiation detection and measurement, including brief description of gas detectors, gamma-detecting instruments, and tomographic scanners.