Pseudomonas aeruginosa is an opportunistic pathogen that causes a wide variety of infections. The cell-density-dependent signaling mechanisms known as quorum sensing play a role in several of these infections including corneal, lung and burn wound infections. In addition, the quorum-sensing systems contribute to the ability of P. aeruginosa to form biofilms on medically important devices. The quorum-sensing systems accomplish their effect by controlling the production of different virulence factors and by manipulating the host immune response.