IEC/TR 61282-4:2013(E) which is a technical report, is intended to describe physically and analytically non-linear effects in fibre optic systems, their impact on system performance, and ways of minimizing the effects or using them to advantage. It contains some of ITU-T Recommendation G.663 with additional material. This second edition cancels and replaces the first edition, published in 2003, and constitutes a technical revision. This edition includes the following significant technical change with respect to the previous edition: clarifications on the compensation for nonlinear impairments with digital signal processing. Key words: physically and analytically non-linear effects in fibre optic systems