It is propitious that the 25th year of publication of the International Journal of Fracture should coincide with the opportunity to support the recognition by the Society of Engineer ing Science of the 65th birthday of the Founding Editor-in-Chief, Professor M.L. Williams. At its 24th Annual Meeting at the University of Utah in September 1987, the Organizing Committee of the Society chose to honor Professor Williams by reserving several sessions for contributions from his colleagues working in the mechanics of fracture and associated mechanical property-structure relationships. We are...