Small-x QCD Effects in Particle Collisions at High Energies

Recent theoretical developments to calculate cross sections of hadronic objects in the high energy limit are summarised and experimental attempts to establish the need for new QCD effects connected with a resummation of small hadron momentum fractions x are reviewed. The relation between small-$x$ parton dynamics and the phenomenon of diffraction is briefly out-lined. In addition, a search for a novel, non-perturbative QCD effect, the production of QCD instanton induced events, is presented.Comment: Invited talk at the XX. Int. Sym. on Lepton and Photon Interactions at High Energies, Rome, Italy, July 200