This Recommendation: gives general information on fundamental types of optical fibre attenuator, their field of application and the main requirements about their Characteristics in terms of optical, mechanical and environmental behaviour; makes a classification of these components in terms of the configurations used in optical fibre plants; reports all the important optical parameters and gives general specifications on the optical, mechanical and environmental performances of optical fibre attenuators; reports the main testing methods of optical fibre attenuators. This Recommendation refers to single-mode optical fibre attenuators only because this fibre is mostly used in present telecommunication systems.