This book constitutes the refereed proceedings of the Third International Symposium on Computing in Object-Oriented Parallel Environments, ISCOPE 99, held in San Francisco, CA, USA in December 1999. The 14 revised full papers presented together with six short papers were selected from 41 submissions. The papers are devoted to compilers and optimization techniques, new application fields, components and metacomputing, numerical frameworks, generic programming and skeletons, application-specific frameworks, and runtime systems and techniques.