Our current understanding of the sophisticated nature of cell-cell communication (quorum sensing (QS)) in the unicellular bacterial world has emerged from elucidating the chemical diversity of QS signal molecules, their biosynthesis, signal transduction mechanisms, target structural genes, turnover and contribution to global regulatory networks within an individual species. This in turn has raised questions with respect the role(s) of QS signals in mixed microbial communities and their impact on higher organisms as well as the evolutionary costs and consequences for QS signal producers and receivers. QS signal molecules have multi-functional properties that impact on host-pathogen interactions and much effort has been devoted to harnessing the translational potential of QS in the context of biosensing, biocontrol, biofouling and synthetic gene circuitry. Since virulence and/or biofilm development is often attenuated in pathogens carrying mutations in key QS genes, there is considerable interest in QS as an antibacterial target. Indications that QS systems are active during human infections have emerged from clinical studies where QS signal molecules are detectable in body fluids and offer potential as biomarkers. Recent work exploiting machine learning in screens for polymers with relevant surface characteristics has highlighted new opportunities for controlling biofilm-associated infections through the inappropriate activation of QS.