Luciferase is the general term given to a class of oxidative enzymes that catalyze reactions that give off light, a process known as bio-luminescence (Fig. 1). In biology, researchers can take advantage of this reaction and use it as a readout for various biological processes. This has perhaps been exploited most in luciferase reporter cell lines where a promoter region from a gene of interest is placed immediately upstream of the coding sequence for luciferase. In this system, transcriptional activation of the gene of interest leads to a level of luciferase expression that is proportional to the level of gene activation.