The ripening of blue and Roquefort cheeses is accomplished by the concerted and controlled actions of enzymes of the mold Penicillium roqueforti. The properties and effects of the enzymes involved in flavor development (i.e., proteases, lipase and beta-ketoacid decarboxylase) are reviewed. The metabolic activities of both spores and mycelia of P. roqueforti in relation to fatty acid metabolism and flavor generation are discussed. The chemical composition of blue cheese flavor and the simulation of this flavor by fermentation and formulation are briefly surveyed. Some nutritional aspects of blue cheese are cited.