Confining glow discharges in submillimeter structures allows us to generate stable, high-pressure, nonthermal plasmas. The gas temperature of such microcavity discharges is relatively low; even for atmospheric-pressure discharges in air, it reaches just 2000 K, and it approaches room temperature when operated in rare gases. Due to the high-pressure operation, even though the plasma is weakly ionized, electron densities on the order of 1015 cm−3 have been reached. Average electron temperatures are on the order of 1 eV. However, the electron energy distribution in these discharges is non-Maxwellian, containing a large concentration of high-energy electrons. The high gas density and the high electron energies allow their use in applications such as excimer light sources and plasma reactors for material processing and due to their low temperature even in plasma medicine. Their resistive characteristics, under certain discharge conditions, allow us to arrange microdischarges in parallel without individual ballast, as well as placing them in series. Using semiconductor microfabrication techniques, this has resulted in the fabrication of large arrays with up to 250,000 microplasmas in parallel. This entry will provide an introduction into the physics of microcavity discharges, their limitations, and their fundamental properties. This is followed by a discussion of a selected group of applications.