Book excerpt: Fracture mechanics is an indispensible tool in the design and safe operation of damage tolerant structures. One of the essential elements in fracture mechanics based analysis is the stress intensity factor. This book provides a powerful theoretical background to the weight function method in fracture mechanics and numerous stress intensity factors. Part I gives a theoretical background and overview of the weight function method. Part II provides further details of the weight functions for various geometries and a large number of stress intensity factor solutions. Part II deals with the determination of crack opening displacements, Dugdale model solutions and crack opening areas.