Rapid development of microfabrication and assembly of nanostructures has opened up many opportunities to miniaturize structures that confine light, producing unusual and extremely interesting optical properties. Microcavities addresses the large variety of optical phenomena taking place in confined solid state structures: microcavities. Realizations include planar and pillar microcavities, whispering gallery modes, and photonic crystals. The microcavities represent a unique laboratory for quantum optics and photonics. They exhibit a number of beautiful effects including leasing, superfluidity, superradiance, entanglement etc.