Spin-, angle- and energy-resolved photoemission with circularly and linearly polarized synchrotron radiation from BESSY has been used to characterize the electronic structure of an Au monolayer on Pt(111). All studies were done with normal radiation incidence and normal electron emission. With [sigma]-radiation the symmetry of the different types of surface and interface states in the Au monolayer on Pt(111) system has been determined. Using [pi]-radiation spin polarized electrons are only found for photoemission from states with symmetry [Lambda] 45 3. One of the states involved in the transition (either initial or final state) was always localized at the surface. In addition to earlier findings of Schmiedeskamp et al. and Stoppmanns et al. spin-polarized electrons are now also obtained for the photoemission from a state which is located only in the Au layer. The spin polarization depends strongly on the energy of the incident radiation.