This book was conceived by Professor K.H. Ephraim, the former director of the Institute for Nuclear Medicine of the University Hospital of Utrecht. Unfortunately, due to a serious illness, he was not able to finish the work he started. He is, however, very pleased to know that the book is, nevertheless, being published. In principle the volume consists of two parts. The first is dedicated to basic science and technology in nuclear medicine. It provides the data which are necessary to a clear understanding of the possibilities and limitations of investigations which make use of radioactive materials. The second part of the book covers those disciplines in medicine in which nuclear medicine can be of help in solving certain clinical problems. Each chapter can be read separately, even without thorough knowledge of the first part of the book. The contributors to this book come from both Europe and North America. Each of them has written his chapter out of long-standing personal interest in his particular field of nuclear medicine. This book will be of value to a wide variety of professionals. It is of interest not only to clinicians of various specialties, but also to diagnostic professionals, i.e. radiologists and nuclear medicine clinicians. Last but not least it will be of use to physicians in training.