This report by the IAEA's International Nuclear Safety Advisory Group INSAG describes the concept of 'Safety Culture' in connection with nuclear plant safety in relation to both organi- zations and individuals engaged in nuclear power activities. It provides a basis for judging the effectiveness of the safety culture in specific cases in order to identify potential improvements. Contents: Summary; 1. Introduction; 2. Definition and character of Safety Culture; 3.1. Requirements at policy level; 3.2. Requirements on managers; 3.3. Response of individuals; 4. Tangible evidence; 4.1. Government and its organizations; 4.2. Operating organization; 4.3. Supporting organizations; 5. Concluding comments; Appendix: Safety Culture indicators.