  We review recent developments in the theory of inflation and cosmological
perturbations produced from inflation. After a brief introduction of the
standard, single-field slow-roll inflation, and the curvature and tensor
perturbations produced from it, we discuss possible sources of nonlinear,
non-Gaussian perturbations in other models of inflation. Then we describe the
so-called $\delta N$ formalism, which is a powerful tool for evaluating
nonlinear curvature perturbations on super Hubble scales.
