This Recommendation identifies the definitions and test methods of performance parameters of the following fibre Raman amplifiers and Raman amplified subsystems: • reverse pumped distributed Raman amplifier; • forward pumped distributed Raman amplifier; • bidirectionally pumped distributed Raman amplifier; • reverse pumped distributed, composite Raman amplifier; • bidirectionally pumped distributed, composite Raman amplifier; • discrete Raman amplifier. This Recommendation describes the classification, the type code, and the reference models of various Raman amplifiers. It also outlines the general characteristics of the Raman amplifiers, and defines the performance and testing parameters for the Raman amplifiers. In this edition of ITU-T Recommendation G.665, Appendix IV was added illustrating Raman amplifiers safety mechanisms.