The introduction to this paper describes a general finite element model used to calculate opening mode stress intensity factors (KI) along the front of an irregular planar crack. Crack advance is calculated as a function of KI and a new profile is thus defined. Automatic reconfiguration of the finite element mesh enables the crack development to be followed. The use of this technique to investigate various problems of practical interest is then described. These examples include the effect of constrained and unconstrained corners on developing cracks, the interaction of two adjacent thumbnail cracks, the breakout of an internally initiated crack and the effect of a surface crack in a leak before break situation.