[en] The basic philosophy of radiation protection, i.e. to prevent non-stochastic effects and to reduce stochastic effects to an acceptable level, is realized in the internationally accepted three-stage system of dose reduction, viz. justification, ALARA and dose limits. Historical development of this three-stage system is described and the three components are worked out further. The application and applicability of the system is considered for radiation sources and accidents. Attention is also given to regulations, national policy and practice of radiation protection. (G.J.P.)