Complete ligament yielding before crack advance is one of the criteria in the essential work method. It is found that this criterion also holds when the essential work method is used to obtain the fracture toughness of polymeric films. This is done by using two specimen geometries to test each of two nylons. The criterion is then used to find the fracture toughness of three polyethylenes, a cast, amorphous poly(ethylene terephthalate) and two kaptons. In addition, the effects of specimen width and strain rate on the specific essential work of fracture w(e) are studied.