This review paper covers the analytical methods used to monitor genotoxic impurities. Specifically, the impurities discussed here contain hydrazine, nitro, arylamine or aldehyde functional groups as found in pharmaceuticals. These genotoxic impurities can come from many places including starting materials, reagents, intermediates, solvents or unwanted side reactions of the active pharmaceutical ingredient (API) synthetic process that get carried over into the final product. In addition, the API itself can decompose to form genotoxic impurities or they can form in the drug product by reaction between excipients or containers and the API. The control of these potent impurities is critical which are generally monitored at very low levels in the ppm and ppb range. This poses many challenges on the analytical methods to achieve high sensitivity as well as separation of the impurities from the sample matrix for selectivity.