This publication is composed of lectures delivered within the framework of the Rosatom Higher School of Physics educational program by a team of radiobiologists led by academician L.A. Ilyin from the leading center for biomedical radiation research - the Federal Medical Biophysical Center named after A.I. Burnazyan FMBA of Russia. The material presented in the book covers the main sections of such a multifaceted scientific discipline as "Radiobiology," from its molecular to the organizational and even social level. The complexity of the task facing the authors predetermined the multilayered style of presenting scientific problems from figuratively popular to approaching highly specialized, moreover, sometimes in the same lecture.