The apparently simple structure known as a planar semiconductor microcavity evidenced a wealth of different effects. Bosonic statistics have given rise to stimulated scattering, polariton lasing, condensation, and superfluidity. Effective magnetic fields, selection rules, and microscopic interactions describe a rich spin sensitivity and the behavior of spin currents. In three-dimensional cavities the quantum nature of the elementary excitations of semiconductor microcavities has yielded quantum squeezing, and the search is on for phenomena such as antibunching and entanglement. Finally, hybrid metal-insulator structures reveal a variety of plasmonic effects which can be used for realization of all-optical integrated circuits.