Physics is the study of matter and energy and the ways in which the two interact. Some physicists use their expertise in physics to focus on radiation. These specialists, called medical physicists and health physicists, work to help people or protect the environment. Medical physicists work with physicians, assisting patients who need imaging technology and radiation treatment in hospitals and other medical facilities. Health physicists protect people or the environment from the potential hazards of radiation in a variety of settings. The first section describes what medical physicists and health physicists do on the job. The second section provides information about employment and wages. And the third section covers skills, training, and certification. Sources for finding more information are at the end of the article.