Abstract: Single-photon sources are a basic resource for the implementation of quantum key distribution and linear optical-quantum computation. In this article, we review the photon statistical properties of light, in particular, single photons and their applications in quantum information science, semiconductor quantum dot based single-photon sources, and the principles of cavity quantum electrodynamics including the coupling between a two-level emitter and an optical cavity in the strong or weak coupling regime. In the weak coupling regime, the spontaneous emission rate can be enhanced by the cavity due to the Purcell effect. We then review the recent development of single-photon sources using single self-assembled quantum dots coupled with optical cavities. Semiconductor cavities employing distributed Bragg reflectors, micropillars and photonic crystals are used to enhance the repetition rate, collection efficiency, polarization and indistinguishability of single photons. Finally, future prospects of semiconductor quantum dot based single-photon sources are discussed.