These proceedings consist of papers presented at the International Workshop organized by the Commission of the European Communities, Joint Research Centre, Ispra Establishment, Department A, in Ispra (Varese) Italy, October 4-6, 1976. Topics addressed in this conference include probabilistic modeling of computer systems, analysis of schedules of computations and tasks, queueing networks, and simulation models. Applications include program behavior measurements and models, scheduling of multiprocessor systems, and reliable processing in the presence of system failures.