This Safety Fundamentals publication provides a coherent set of objectives and principles for protection against ionizing radiation and for ensuring safety in the use of radiation sources. The protection objective and the safety objective, together with the eleven principles that have to be applied to achieve them, represent an international consensus. They provide the basis for the requirements in IAEA Safety Standards for the control of occupational, public and medical exposures and for the safety of sources. The Safety Fundamentals also provide an insight into the general system of protection and safety for those at senior levels in government and regulatory bodies and those responsible for making decisions relating to the uses of radiation in medicine, industry, agriculture, research and other areas. Contents: 1. Introduction; 2. Biological effects of irradiation; 3. Objectives of protection and safety; 4. Principles for practices; 5. Principles for intervention; 6. Implementation principles; 7. Infrastructure for protection and safety; Definitions.Chinese, French, Russian and Spanish editions in preparation.