The quantities describing constraint and triaxiality and their relation with each other are discussed for various loading conditions and specimen geometries by comparing numerical simulations of crack growth based on the J-integral concept and on micromechanical damage models with the corresponding experiments. It is shown that the geometry dependence of JR-curves is a natural feature due to different patterns of plastic flow and microchemical processes depending on the local stress state. Hence, this dependence cannot and should not be overcome by manipulating the definition of J. A pragmatic definition of a local triaxiality parameter is given that gives reliable and reproducible results. A linear relationship is found between the triaxiality and the tearing modulus of various specimens of the same material.