The essential work of fracture method is explored. The method was used to determine the fracture toughness of a series of toughened polymer blends and the crack resistance of a thin ductile polymer film, which could not be tested using the J-integral method. A comparison between J-integral and the specific essential work of fracture was carried out to test the equivalence of the two methods, The effects of geometry on the essential work of fracture and the plane-stress/plane-strain transition were studied. It has been shown that the specific essential work of fracture is a material constant, independent of sample geometry, and equivalent to the critical J-integral. The plane-stress/plane-strain transition is found to depend on the nature of the material tested. The sample thickness requirement for valid plane-strain specific essential work of fracture is discussed, and it is proposed that the size requirement for the plane-strain specific essential work of fracture may be less rigorous than that for plane-strain J(IC) measurement.