This report addresses the development and implementation of computerized operator support systems (COSS) in nuclear installations. It discusses the requirements of operators in information management and job performance in control room environments. The design methodology described presents good practice approaches derived from the experience gained and the lessons learned during actual development of the COSS. Contents: 1. Introduction; 2. Computerized operator support systems; 3. Operational requirements; 4. Design methodology; 5. Verification and validation; 6. Implementation; 7. Licensing considerations; Appendix I: Classification scheme for man-machine activities; Appendix II: Techniques.