  Results on isolated prompt photon production are presented. The measurements
were performed at HERA in deep inelastic ep scattering and photoproduction, as
well as at LEP in photon photon collisions. Differential cross sections are
shown for inclusive prompt photons and those accompanied by a jet. The results
are compared to predictions of perturbative QCD calculations in next to leading
order and to predictions of the event generators PYTHIA and HERWIG.
