AbstractCrack velocity measurements and fracture toughness tests have been carried out on extruded sheets of bisphenol‐A polycarbonate. Slow bend tests provided quasi‐static K1c data while dynamic initiation values were obtained from instrumented Charpy impact tests. In both types of tests high‐speed crack velocity measurements were made using conductive silver grids applied to the specimens. The variation of K1c with strain rate and temperature was found to be small and in general agreement with expectations from the relaxation properties of polycarbonate. Notch acuity was found to have little effect in that values of K1c and crack velocity from specimens having the standard Charpy notch were similar to values obtained from sharp‐cracked specimens. Some anisotropy was present in the material and gave rise to a small variation in K1c values with direction of crack propagation. Crack velocity and also the fracture mode transition temperature showed considerable dependence upon orientation. It was thought that dynamic toughness Kd, was influenced more than K1c by partial orientation of amorphous regions in the material and that the relaxation time for re‐orientation was probably significant here.