The updated edition of the second of three volumes on Medical Physics presents modern physical methods for medical diagnostics. It provides a solid background on imaging techniques that use non-ionizing probes (ultrasound, endoscopy including CLE and OCT, MRI) and imaging techniques that use ionizing radiation (X-ray radiography, CT, SPECT, PET). Radiation sources, interactions of radiation with matter and radiation protection for x-rays, -rays, protons and neutrons are presented. Some of these topics are also relevant to the therapeutic applications presented in Volume 3. NEW: highlighted boxes emphasize specifi c topics; math boxes explain more advanced mathematical issues; each chapter concludes with a summary of the key concepts, questions, a self-assessment of the acquired competence and exercises. The appendix provides answers to questions and solutions to exercises.