An attempt has been made to apply the concepts of fracture mechanics to describe the behaviour of a paper sheet with a crack. Considering paper as an orthotropic homogeneous continuum, the critical strain energy release rate, G c, for eight different papers has been measured using linear elastic fracture mechanics. Also, a direct measurement of work of fracture, R, has been made for these samples by using the quasi-static crack propagation technique. For both techniques, results independent of specimen dimensions were obtained. G c and R were found to be experimentally equivalent. The fracture toughness of paper has been compared with that of other engineering materials.