Inflationary Prediction for Primordial Non-Gaussianity

We extend the δN formalism so that it gives all of the stochastic properties of the primordial curvature perturbation ζ if the initial field perturbations are Gaussian. The calculation requires only the knowledge of some family of unperturbed universes. A formula is given for the normalization f_NL of the bispectrum of ζ, which is the main signal of non-Gaussianity. Examples of the use of the formula are given, and its relation to cosmological perturbation theory is explained.