This document discusses the effective field theory of multi-field inflation based on Weinberg's approach. It constructs the most general Lagrangian for the background and perturbation terms up to fourth order. For the multi-field case, the Lagrangian contains terms for both the adiabatic and entropy perturbations. The validity of the effective field theory constrains the possible amplitude of non-Gaussianities produced during inflation. This approach differs from previous work by defining perturbations before distinguishing adiabatic and entropy modes.