The Origin of Matter in the Universe: Reheating after Inflation

In the inflationary scenario all the matter constituting the universe was created from the process of reheating after inflation. Recent development of the theory of reheating is briefly reviewed. The list of topics includes elementary (perturbative) theory of reheating; quantum field theory in a time-varying background; parametric resonance and explosive particle creation; non-thermal phase transitions from reheating; baryogenesis from reheating; residual oscillations of the scalar field, and other cosmological applications.