The ability to communicate and coordinate group behavior has been traditionally attributed only to the higher organisms. Microbes have been considered too simple to be capable of such complex social interactions. This view has changed with the discovery of cell-to-cell communication, called quorum sensing. By quorum sensing, bacteria coordinate their actions with other members of the microbial community. This allows them to complete tasks that would be otherwise hard or completely impossible to accomplish for a single bacterium. Quorum sensing is important for intra-species, inter-species as well as for inter-kingdom communication. Communication between pathogenic bacteria is important for establishing and maintaining an infection. Development of novel antimicrobial drugs blocking communication between microorganisms is therefore crucial for the ongoing fight against current and emerging pathogens.