It is presented the J-integral concept, introduced by Rice as a crack-parameter when LEFM is no more valid. Considering J as an extension of the linear theory, it has a direct correlation with K. Two methods for obtaining J are described, the line integral, following strictly the J definition, and the nonlinear energy release rate. Also, it is introduced the EPRI procedure to obtain the applied J for a given cracked geometry, where J is considered as a sum of two portions, an elastic and a plastic one. Besides, the tearing modulus T is presented along with the J/T methodology that correlates J and T. At the end, a brief discussion is done about the use of cyclic J, as a parameter to estimates the crack propagation under fatigue when the level of plastic strain may prevent the application of Paris law.