  In this review, we discuss how non-Gaussianity of cosmological perturbations
arises from inflation. After introducing the in-in formalism to calculate the
$n$-point correlation function of quantum fields, we present the computation of
the bispectrum of the curvature perturbation generated in general single field
inflation models. The shapes of the bispectrum are compared with the local-type
non-Gaussianity that arises from non-linear dynamics on super-horizon scales.
