Quorum sensing (QS) is a chemical communication process that bacteria use to orchestrate group behaviors. QS involves the production, release, and population-wide detection of signaling molecules called autoinducers. QS-controlled behaviors are unproductive when undertaken by a single bacterium but become effective when performed by the group. This SnapShot highlights model QS circuits, the molecules used for communication, QS-controlled behaviors, and exciting future challenges. To view this SnapShot, open or download the PDF.