Confined photon system such as microcavities and photonic crystals are currently of great interest, both in terms of fundamental physics and as a result of potential applications. They enable the study of low-dimensional photonic systems, modified light-matter interaction, e.g. between excitons and photons in all-solid-state semiconductor microcavities, and of many phenomena of quantum optics, including single photon generation, squeezed light, quantum state entanglement, non-local quantum measurements, and, potentially, quantum computation. They are also on the verge of yielding new, high performance optical devices for large-scale industries such as telecommunications and display technology. The lectures in this book are organized in a didactic fashion, with a group of in-depth introductory lectures followed by more specialist contributions detailing particular applications of confined photon systems.