Quorum sensing (QS) is a cell density-dependent system of bacterial communication used by several species for triggering a coordinated response when the population reaches a given cell density threshold. Basically, the QS regulatory circuits are formed by two elements, one signal molecule that is constantly produced, and a transcriptional regulator, which activity depends on the presence of a given concentration of the signal molecule. This allows the coordinated expression by the bacterial population of specific sets of genes involved in processes relevant for microbial physiology as the control of the production of secondary metabolites, motility, biofilm formation or the production of virulence determinants among several others.