Quorum sensing is an important mechanism for the transmission of information among bacteria through chemical signal molecules. This chapter reviews the composition, signal transduction mechanism, and regulation of biofilm formation by the quorum sensing system. The quorum sensing system of lactic acid bacteria AI-2/LuxS and its role in the regulation of biofilm formation and autolysis is also reviewed. This review will provide new ideas in improving the fermentation density of lactic acid bacteria, as well as expanding their probiotic functions.