This volume is the product of Lecturers in the fourth Course of the International School of Cosmic-Ray Astrophysics held at the Ettore Majorana Center in Erice, Sicily in November, 1984. The Course, devoted to "Cosmic Radiation in Contemporary Astrophysics," was concurrently a NATO-sponsored Advanced Study Institute (ASI). Cosmic-ray research is in a state of ferment. Precise measure ments - some made with instruments aboard sattelites and space probe- have been confronting models and theories with severe constraints. The observations of gamma-ray sources, notably Cyg X-3, at energies up to...