X-rays were discovered by Roentgen in 1895, and ever since, the ionizing radiation has been largely used in various industrial as well as medical applications. However, its harmful characteristics are gradually recognized through accidental uses. The experience of nuclear power plant mishaps in Fukushima and Chernobyl, has unveiled the risk of ionizing radiation and its prevalence in our contemporary society. Therefore, it is extremely necessary that more engineers, students and scientists become known to ionizing radiation research regardless of the research field they are engaged in. On the basis of this idea, this book was formulated to analyze the current achievements in this field inclusive of medical uses, principles of radiation measurement, and its impact on health.