The photon is a very good probe of short distance physics in strong interactions. It can be produced directly at short-distance or through fragmentation processes. Through one-loop order in perturbation theory of quantum chromodynamics (QCD), this thesis provides complete analytic expressions for both the inclusive and the isolated prompt photon production cross sections in hadronic final states of e+e- annihilations. It is the first time that the full angular dependence of the cross sections is derived. Extraction of photon fragmentation functions from e+e- annihilations is addressed. Using e+e-→[gamma]+X as an example, this work demonstrates for the first time that conventional perturbative QCD factorization breaks down for isolated photon production in e+e- annihilations in a specific region of phase space. The impact of this breakdown for computations of prompt photon production in hadron-hadron reactions is also discussed. In hadron-nucleus collisions, high energy photons can be produced through a single hard scattering as well as through multiple scattering. The contribution from the multiple scattering can be presented in terms of multi-parton correlation functions. Using information on the multi-parton correlation functions extracted from photon-nucleus experiments, for the first time, the nuclear dependence of direct photon production in hadron-nucleus collisions was predicted without any free parameter, and was tested at Fermi Lab experiment E706
