A fracture test using the single edge notch (SEN) geometry was developed for thin polymeric films. The SEN specimens were videotaped while they were stressed to fracture within an Instron tensile testing machine operating at a constant cross-head speed. Critical stress intensity factors for fracture instability and for the initiation of crack growth, along with the corresponding fracture energies, were obtained using a residual stress analysis. The method is applicable to brittle films and films of moderate ductility. Critical stress intensity factors ranging from 0.12 to 4.03 MPa root m were determined for thin films under plane stress conditions. Results of the test are presented for poly(di-n-hexylsilane), Kapton polyimide, polystyrene, and Trycite biaxially oriented polystyrene film. Validation of the test and interpretation of the results are also discussed.