Aspects of Preheating after Inflation

In inflationary cosmology, the particles constituting the Universe are created after inflation in the process of reheating due to the interaction with the oscillating inflaton field. We briefly review the basics of the slow reheating, and the stage of fast preheating, when the particles are created explosively in the regime of parametric resonance. The non-perturbative, out-of-equilibrium character of the parametric resonance changes many features of reheating. For these proceedings, we will highlight a few aspects of preheating: the structural dependence of the parametric resonance on the inflationary model, including $V(\phi)={m^2 \over 2}\phi^2$, ${\lambda\over 4}\phi^4$, $1-\cos {\phi \over f}$; ``rescattering'' of created particles; and phase transitions after inflation.