Ionizing radiation has been revolutionizing the diagnostic process in medicine. However, its use is not without risk, necessitating protection of patients and staff from potential harm. The amount of radiation patients receive continues to rise, mainly due to the use of high-dose examination techniques such as computed tomography and image-guided interventional procedures. In some countries, the amount of radiation a population receives from medical use is already larger than that from natural background radiation. Therefore, a basic knowledge of radiation effects on the human body, radiation protection principles, and relevant legislation is of great importance to all clinicians. This will enable doctors to assess potential risks associated with ionizing radiation in medical imaging and to make an informed choice when different investigations are available to assess a patient.