From particle physics to medical applications CERN is the worlds largest particle physics research laboratory. Since it was established in 1954 it has made an outstanding contribution to our understanding of the fundamental particles and their interactions and also to the technologies needed to analyse their properties and behaviour. The experimental challenges have pushed the performance of particle accelerators and detectors to the limits of our technical capabilities and these groundbreaking technologies can also have a significant impact in applications beyond particle physics. In particular the detectors developed for particle physics have led to improved techniques for medical imaging while accelerator technologies lie at the heart of the irradiation methods that are widely used for treating cancer. Indeed many important diagnostic and therapeutic techniques used by healthcare professionals are based either on basic physics principles or the technologies developed to carry out physics research. Ever since the discovery of x rays by Roentgen in 1895 physics has been instrumental in the development of technologies in the biomedical domain including the use of ionizing radiation for medical imaging and therapy. Some key examples that are explored in detail in this book include scanners based on positron emission tomography as well as radiation therapy for cancer treatment. Even the collaborative model of particle physics is proving to be effective in catalysing multidisciplinary research for medical applications ensuring that pioneering physics research is exploited for the benefit of all.