This set of lecture notes provides a detailed and up-to-date description of a field undergoing explosive growth, that of confined photon systems in the shape of microcavities or photonic crystals. Bringing together world leaders in the field, it provides all the basic tools needed to master a subject which will have both major impact in fundamental studies and widescale applications. Confined photon systems 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...