The aim of the Karlsruhe Tritium Neutrino (KATRIN) experiment is a neutrino mass measurement with a sensitivity of 0.2 eV/c2 (90% C.L.) by the investigation of tritium beta-spectrum. It requires the continuous monitoring of the isotopic composition of the tritium gas by Raman spectroscopy. The aim of this work was to design and commission the Raman system. Special emphasize was put on the metrological performance and reliable operation over the projected operating time of several years.