The collisions of high energy photons produced at a electron-positron collider provide a comprehensive laboratory for testing QCD, electroweak interactions and extensions of the standard model. The luminosity and energy of the colliding photons produced by back-scattering laser beams is expected to be comparable to that of the primary e[sup +]e[sup [minus]] collisions. In this overview, we shall focus on tests of electroweak theory in photon-photon annihilation, particularly [gamma][gamma] [yields] W[sup +]W[sup [minus]], [gamma][gamma] [yields] Higgs bosons, and higher-order loop processes, such as [gamma][gamma] [yields] [gamma][gamma], Z[gamma] and ZZ. Since each photon can be resolved into a W[sup +]W[sup minus] pair, high energy photon-photon collisions can also provide a remarkably background-free laboratory for studying WW collisions and annihilation. We also review high energy [gamma][gamma] tests of quantum chromodynamics, such as the scaling of the photon structure function, t[bar t] production, mini-jet processes, and diffractive reactions.