This technical report gives a short summary of the radiation exposure in certain environments and applications and the different radiation effects on fibres. It also describes the most important radiation effect, i.e. the increase of transmission loss, and its strong dependence on a variety of fibre properties and test conditions. These dependencies need to be known in order to perform appropriate tests for each specific application as well as to understand, compare and qualify the test results obtained at different laboratories when performed according to IEC 60793-1-54, Optical fibres – Part 1-54: Measurement methods and test procedures – Gamma irradiation.