Polarization mode dispersion (PMD) remains the most important limiting impairment for high bit rate transmission over optical fibers. In this article, after a brief description of PMD model and the associated statistic, we study the pulse distortion due to PMD using a powerful time-frequency diagram. This approach allows a very simple illustration of the second and high order PMD effects through effective pulse broadening. Finally, the PMD emulation issue and both electronic and optical compensation techniques are presented, that is a current field of cooperation between ENST-Bretagne and France Telecom R&D.