Direct photon production in hadronic interactions

Theoretical and experimental investigations of direct photon production in hadronic interactions are reviewed. The formalism for the lowest-order quantum chromodynamics calculations is outlined and qualitative predictions are presented. Uncertainties and corrections to the theory are discussed. A review of the experimental techniques is followed by a summary of recent experimental data. Advances in the study of the structure of direct photon events and of the production of pairs of direct photons are summarised. (author)