A full-wave, integral equation method is presented which generalizes the treatment of multi-layer substrates and superstrates for shielded circuits so that any combination and number of layers can be handled without reformulation. A vector wave function approach with dyadic analysis is used to expand the fields, producing all components of the dyadic Green's functions in one solution. The approach makes application to the analysis of shielded transmission lines very straightforward including the calculation of the fields in all layers. Application to the determination of fundamental properties of strip transmission lines are emphasized in the examples provided.