This volume contains the proceedings of the USA-Japan Joint Seminar on "Fracture Mechanics of Ductile and Tough Materials and Its Applications to Energy Related Structures". The seminar was supported jointly by the National Science Foundation of the United States and the Japan Society for the Promotion of Sciences. The seminar was held from November 12th to 16th, 1979, at Hayama, Japan, a picturesque resort town by the beach of Sagami Bay facing Mt. Fugi. The safety and integrity of the engineering structures for energy explora tion, energy production, and energy transportation are of utmost importance to our welfare. Both the United States and Japan are at the forefront of the re search on fracture mechanics and its applications to fracture prevention. Dur ing the past few years, major research efforts have been made in the areas of non-linear fracture mechanics and its applications to fracture initiation, slow crack growth, creep and fatigue. This joint seminar offered an unique opportunity for detailed exchange of information on current researches and fu ture efforts.