Medical Physics is the application of the physics to medicine, pursued by medical physicists, that uses physics principles, methods and techniques in practice and research for the prevention, diagnosis and treatment of human diseases with a specific goal of improving human health. The field of medical physics started with the discovery of X-rays and radioactivity in the 1890′s. Physicists were also pivotal in using radiation as a treatment for cancer. We can be very proud that Canadian physicist, Harold Johns (1915-1998), developed in the late 1940s the first Cobalt Therapy Unit. Medical physics may be classified into a number of sub-fields (specialties), including Radiation Oncology Physics, Medical Imaging Physics, Nuclear Medicine Physics and Radiation Protection in Medicine). It is also linked to sciences such as Biophysics, Biological Physics, and Health Physics. Ultrasound, Magnetic Resonance Imaging, Computed Tomography, Nuclear Medicine, X-rays, Radiation Therapy, are all branches of medical physics