Recently the authors have derived new types of path independent integrals in which the theoretical limitations of the so-called J integral are overcome. For elastodynamic crack problems, a path independent integral J' (dynamic J integral) which has the physical meaning of energy release rate was derived. Later the J' integral was extended to a more general form of the path independent integral T* (generalized J integral) which is valid for any constitutive relation under quasi-static as well as dynamic conditions. This paper presents recent developments in a series of studies on the T* integral in nonlinear and dynamic fracture mechanics. The first study concerns the behavior of the T* integral in an elastoplastic dynamic fracture initiation test specimen. The T* integral exhibits excellent path independency despite the impact loadings and large plastic deformations. The second study reveals the invariance of the T* integral with respect to the shapes and sizes of the fracture process zone. The last study shows the methodology of a direct measurement of the T* integral using the method of caustics (shadow pattern method). These results serve to illustrate the validity of the T* integral as a unified crack-tip parameter for various types of fracture mechanics problems.