This module examines how radiation affects public health. Starting from basic physics and biology of radiation interactions with materials and tissues, resultant radiation regulations and policies will be scientifically justified, with selected examples in the Canada/Ontario hospital settings. Effective protection from natural or artificial radiation sources, using time, distance and shielding principles, will be covered. Radiation detectors and dosimetry will be presented. Safety design aspects of radiotherapy vaults, radiology rooms, and radiation research laboratories will be a major focus of the second part of the course. Visits to the UHN Nuclear Medicine labs and radiation therapy treatment vaults will provide practical context for these concepts.