Quorum sensing (QS) is a phenomenon that microbes regulate some of their genes by signals related to the density of population. It is confirmed that acyl-homoserine lactones (AHL), some peptides, some furanones and some other small moleculars can be used as quorum-sensing signals by microbes. Microbes control their physiology with different QS systems in parallel or hierarchical ways. A lot of microbial pathogenesis connect with quorum sensing closely. More and more studies show that QS systems regulate microbial pathogenesis through the following points: (1) QS helping pathogens invasion and colonization; (2) QS regulating production of virulent factor; (3) QS giving pathogens the ability of immunity or drug resistance. We review the role of QS in microbial pathogenesis and address a new way to prevent and control microbial diseases.