This publication, Cracks and Fracture, contains papers presented at the Ninth National Symposium on Fracture Mechanics which was held at the University of Pittsburgh, Pittsburgh, Pa., 25-27 Aug. 1975. The Symposium was sponsored by Committee E24 on Fracture Testing of Metals of the American Society for Testing and Materials. J. L. Swedlow, Carnegie-Mellon University, and M. L. Williams, University of Pittsburgh, presided as symposium co-chairmen.