Since the best route to adhesion is through chemical bonding, the knowledge of which of the chemical groups present on the surface of a plastic lead to good adhesion is essential for defining the proper paint/plastic combination. To answer this question we studied corona and UV surface modification of several engineering resins, and its effect on the adhesion of a two component polyurethane paint. In every case such surface modification led to a substantial improvement in adhesion. To determine which functional groups were responsible for this improvement, plasma polymerizations on the neat resins were carried out in an attempt to produce a specifically functionalized surface. The amount of the given functional group within the plasma polymerized films was measured by XPS. From this information and the amount of paint adhesion to these plasma modified surfaces it was concluded that the -OH and possibly -CHO groups are most desirable in promoting adhesion to the two component polyurethane paint.