Large number of sensitizers and protectors of cells, tissues, organs and organisms are being discussed in this review. Attention is paid to metals, nanoparticles or organic compounds as modifiers. They can modify the radiation sensitivity by 20–60%. In most cases, sensitization is caused by an increase in DNA damage or a decrease in the repair of radiation damage. The protection can be caused in many cases by repair of damaged DNA molecules, proteins or enzymes, or by reducing the ROS concentration. The most current research tasks in this area are formulated. A new quantitative and reproducible method of evaluating modifiers is discussed.