Modern proton therapy is saving the lives of more and more children and adults with difficult-to-treat cancers. The spectacular rise of proton therapy might never have happened if it were not for the pioneering work of the Paul Scherrer Institute - a Swiss centre founded to explore physics and the nature of matter, but which turned its understanding of basic science into applications that would benefit mankind. This is the place that pioneered a technique of delivering protons to tumours called pencil beam scanning (also known as spot scanning) - now used in nearly every proton therapy centre in the world. It also developed techniques to more accurately deliver the correct proton dose to every part of a tumour - again, now used globally. This book is for anyone with an interest in scientists' continual quest to find out more. It tells the remarkable story, spanning half a century, of the men and women at the Paul Scherrer Institute's Center for Proton Therapy who had the knowledge, imagination and perseverance to bring their ideas to fruition. It demonstrates, perhaps most of all, just what can be achieved from close collaboration between physicians and scientists - bringing all the powers of physics to bear in the fight against cancer. "For a field to grow, and for the community of patients to be best served, it's necessary to learn, grow, improve and share, the way it has been done at PSI. This book provides a look at that extremely important perspective. I, for one, read it with great pleasure." (Jay Flanz, Project Director and Technical Director of the Burr Proton Therapy Center, Massachusetts General Hospital)