This chapter explores biodeterioration problems, to present a variety of case histories involving the application of adenosine triphosphate (ATP) luminescence to biodeterioration studies, and to indicate how developments in ATP-related technology may potentially be applied in future investigations of biologically induced spoilage. Materials subject to biodeterioration range from surface coatings to rubbers and plastics, from fuels and lubricants, to metals and stone. The direct and indirect consequences of biodeterioration may be considerable in terms of financial and material losses. The use of various staining techniques is obviously important in microbial ecology and biodeterioration studies. Most biodeterioration investigations require initial detection of biodeteriogen activity, an estimate of the severity of attack, and confirmation of remedial treatment efficacy. The basic protocol involves sample preparation, extraction of somatic ATP, removal of somatic ATP, extraction of microbial ATP, and assay via addition of luciferase reagent and measurement of light emission.