In the modern analytical laboratory UV/VIS spectroscopy is an indispensable method that is well established, reliable and accurate. UV/VIS spectrometers must be checked regularly for correctness and uniformity of results and function and documented as such. This is obligatory when working according to DAB or Ph. Eur., but also when working according to GLP, GMP, USP and DIN EN ISO 9001:2000 or DIN EN ISO/IEC 17025. Absorbance, stray light, spectral resolution power and wavelength accuracy are the parameters that can be determined using UV/ VIS standards according to Ph. Eur.