  We present here the zero curvature formulation for a wide class of field
theory models. This formalism, which relies on the existence of an operator
$\d$ which decomposes the exterior space-time derivative as a BRS commutator,
turns out to be particularly useful in order to solve the Wess-Zumino
consistency condition. The examples of the topological theories and of the
$B$-$C$ string ghost system are considered in detail.
