The basic features of this family of techniques are discussed, beginning with its historical development. Angle-resolved (band mapping) and angle-integrated techniques are analyzed as well as a series of experimental approaches requiring powerful photon sources such as undulators at synchrotrons or free electron lasers. Such techniques include photon polarization spectroscopy, experiments with variable photon energy, photoemission resonances and techniques affected by low signal levels such as time-resolved photoemission, two-photon photoemission, spectromicroscopy and spin-polarized photoemission. Finally, high-resolution photoemission studies of superconductors and of other highly correlated systems are briefly discussed.