The present publication is an update of IAEA Technical Reports Series No. 235, Status of and Prospects for Gas-Cooled Reactors, published in 1984. It is a compilation of information based on submissions from Member States and is considered current as of the beginning of 1989. It describes the status of gas cooled reactors with specific emphasis on the design and safety characteristics of the various concepts that are either incorporated in operating reactors or in reactors being designed and considered for future construction and operation. Contents: Chapter 1. Introduction; Chapter 2. Status of international gas cooled reactor development; Chapter 3. General features of gas cooled reactors and their safety characteristics; Chapter 4. Gas cooled reactor design and safety in the United Kingdom; Chapter 5. Gas cooled reactor design and safety in the United States of America; Chapter 6. Gas cooled reactor design and safety in Japan; Chapter 7. Gas cooled reactor design and safety in the Union of Soviet Socialist Republics; Chapter 8. Gas cooled reactor design and safety in Switzerland; Chapter 9. Gas cooled reactor design and safety in the Federal Republic of Germany; Chapter 10. Summary; Annex: Information exchange on gas cooled reactors.