Cell-to cell communication occurs via a signaling pathway referred to as quorum sensing. There are four main types of these systems according to the chemical nature of signal molecules used by microorganisms to elicit expression of target genes in response to environmental stimuli or need of microbial communities. Type I system acts by using acyl homoserine lactones as signals to trigger the expression of virulence genes in Pseudomonas aeruginosa and members of the Enterobacteriacae family. Other groups of bacteria possess a second system which uses certain furanones as a universal language among different species. Pathogenic Shigella spp., Salmonella, and Escherichia coli rely on catecholamines of the human host for inducing a third quorum sensing system in infection. Short cyclic peptides act mainly in Staphylococcus spp. and Enteroccocus faecalis to activate a forth system involved in their pathogenicity. Therefore, it is essential to analyze these systems for the design of antimicrobials that could eliminate pathogens or abolish their harmful activities.