Pyrene (Py) and various metabolites with a Py chromophore are powerful probes often used in biophysical and biochemical sciences due to their high fluorescent quantum yields and relatively long fluorescence lifetimes. In this book, the authors present current research in the study of the chemical properties, biochemistry applications and toxic effects of pyrene. Topics include the biological effects induced by benzyprene in soil and plants; benzo(a)pyrene and colonic cancer; bacterial metabolism of pyrene; low-temperature laser-induced fluorescence studies of various biological systems with pyrene chromophore; photo-energy and electron donating ability of pyrene; and synthesis of novel silylated pyrene units and their application as a fluorescent labeling agent for bioactive components such as oligodna and cholesterol.