This report outlines the characteristics of heavy water reactors and provides an insight into the technology for specialists in countries where the establishment of nuclear power programmes is being considered. It should serve as a reference for engineers and scientists working in the field, as well as for lecturers in nuclear technology. Contents: Section 1. Introduction; Section 2. HWR evolution; Section 3. Characteristics of HWRs; Section 4. Economics of HWRs; Section 5. Safety aspects of HWRs; Section 6. HWR fuel cycles; Section 7. Environmental considerations; Section 8. Vision of advanced HWR designs; Appendix: Parameters of the principal types of HWR.