In the seismic design criteria for highway bridges, there is a significant lack of guidance on ways to incorporate the effect of soil-structure interaction in determining seismic response. For this study, a simple analytical model for pile and pile group foundations is presented for use in dynamic modeling of bridge superstructures. Both the axial and lateral pile response is considered. This simple model consists of a set of nonlinear springs, dampers, and masses for each degree-of-freedom of the pile, and it is based on the Winkler hypothesis. The spring behavior was established by using the finite element method for static load conditions and a typical soil from Washington state. The lumped damping constants and masses were based on realistic approximations. The p-y and t-z curves for single piles and two-pile groups were presented for two pile diameters. Using these curves as near-field Winkler elements, combined with established far-field elements, the dynamic response of a single pile when subjected to a half-sine impulse load was compared to that of a more rigorous, nonlinear, three-dimensional finite element analysis. Close agreement was observed. For design, suggestions were made on ways to develop an approximately equivalent foundation model consisting of a single mass, spring, and damper.