This course is the first of three focused on radiation therapy physics. The topics covered are theoretical and experimental aspects of radiation therapy physics. Production of x-rays, clinical radiation generators, interactions of ionizing radiation with matter, methods of radiation dose measurement, and measurements of absorbed dose are some of the topics covered in the course. The concepts employed in radiation therapy dose calculations are also covered. This course is intended for medical physics graduate students and medical residents but is open to graduate and upper level undergraduate students in related fields.