Fracture behaviour of an amorphous polyethylene terephthalate (PET) film with a glass transition temperature (T-g) of 72degreesC and a thickness of 0.21 mm was studied between 23 and 70degreesC using Double Edge Notched Tension (DENT) specimens. Within this temperature range, DENT specimens fractured by ductile tearing of the ligament region after ligament region had been fully yielded. The load-displacement curves obtained for different ligament lengths were geometrically similar to one another. On the basis of these, Essential Work of Fracture (EWF) methodology was used to determine fracture toughness of the PET film as a function of temperature. A linear relationship was obtained between the total specific work of fracture, w(f), and ligament length, L, at temperatures under consideration. Results showed that specific essential work of fracture, w(e), is independent of temperature but the specific non-essential work of fracture (beta w(p)) increases with increasing temperature and drops in value near the glass-transition temperature. A linear relationship was also found for yielding (w(y)) and necking/tearing (w(n)t) components of w(f) as a function of ligament length. The specific essential work components were found to be temperature dependent and whilst component w(e)y decreased component w(e)nt increased with increasing temperature. The contribution of w(e)nt to w(e) was substantially greater than that of w(e)y at all temperatures.