 Exotons, quasi-particles of tightly bound electron-hole pairs, dominate the optical response of atomically thin-transitioned metal decalcogenides. Here, the authors review strong light matter coupling in two-dimensional semiconductors arising from confined exotons interacting with trapped photons or localized plasmas. This article was authored by Christian Schneider, Mikhail M. Glazov, Tobias Korn, and others.