This technical report applies to all commercially available fibre optic products sensitive to polarization mode dispersion (PMD). This report presents general information about PMD, the mathematical formulation related to the application of the generally accepted methods to test PMD, and some considerations related to the sampling theory regarding the use of different light sources and detection systems. This report is complementary to the International Standards describing the PMD procedures (IEC 60793-1-48, IEC 61280-4-4, IEC 61290-11-1, IEC 61290-11-2 and IEC 61300-3-32) and other design guides on PMD (IEC 61282-3 and IEC 61292-5).