These volumes, 5 and 6, of Fracture Mechanics of Ceramics constitute the proceedings of an international symposium on the fracture mechanics of ceramic materials held at The Pennsylvania State University, University Park, PA on July 15, 16, and 17, 1981. These proceedings constitute the third pair of volumes of a con- tinuing series of conferences. Volumes 1 and 2 were from the 1973 symposium and volumes 3 and 4 from a 1977 symposium, both of which were also held at Penn State. The theme of this conference, as the previous two, focused on the mechanical behavior of ceramic materials in terms of the characteristics of cracks, particularly the roles which they assume in the fracture process. The 78 contributed papers by over 100 authors and co-authors represent the current state of the field. They address many of the theoretical and practical problems of interest to those concerned with brittle fracture. The program chairmen gratefully acknowledge the financial assistance for the Symposium provided by the Army Research Office, the National Science Foundation, and the Office of Naval Research. Without their support, the magnitude and quality of this conference simply would not have been possible.