  Effective field theory provides a perturbative framework to study the
evolution of cosmological large-scale structure. We investigate the
underpinnings of this approach, and suggest new ways to compute correlation
functions of cosmological observables. We find that, in contrast with quantum
field theory, the appropriate effective theory of classical cosmological
perturbations involves interactions that are nonlocal in time. We describe an
alternative to the usual approach of smoothing the perturbations, based on a
path-integral formulation of the renormalization group equations. This
technique allows for improved handling of short-distance modes that are
perturbatively generated by long-distance interactions.
