Abstract: A simplified plastic window framing system for single or multiple glazing comprising combinations of complementary extrusions wherein the outward appearance of the finished mullions and peripheral framing appears to be that of single extrusions. In outward appearance the glazing is retained within recesses formed in the mullions or frame members and separable retaining members. The combination creates a substantially rectangular external appearance to the individual mullions and framing members.The framing members are roughly L-shaped and the mullions are roughly T-shaped in cross section. The retaining members are substantially rectangular or trapezoidal in cross section. As finished units however, the mullions and framing members are both substantially rectangular in cross section with only the co-extruded glass seals slightly protruding from the mullions or framing members.