There are three sections in this e-learning module on radiation emergencies: Section One is an introduction about the basics of radiation. For instance, the difference between ionizing and non-ionizing radiation and the different ways to measure radiation. Section Two is about the health effects of acute exposure to radiation. For instance, the mechanisms by which ionizing radiation damages our cells and the clinical manifestations of acute exposure are introduced. Section Three discusses the measures in response to a radiation emergency. For instance, the principles of emergency department preparedness, the use of personal protective equipment and the procedures to decontamination are presented. Although this module is primarily for first responders to prepare for radiation emergencies, it is also suitable for the general public who are interested in knowing more about this topic. Healthcare professionals may also find this module useful in case they want to refresh their knowledge on radiation.