Physics aims at explaining and describing as many processes of nature as possible. In this book the authors show several examples of its usefulness in the medical environment. The authors start from basic processes like bacterial diffusion, eye vision, through preclinical applications, to radiation treatment planning. This sampling allows profound examination of powerful tools, which physics provide for medical field. This book is intended for medical students at the doctoral or post-doctoral level, students of medical physics of master level or higher, or for medical doctors who want to have a deeper insight into their specialty.