This book contributes the thoroughly refereed post-proceedings of the Third International Workshop on Power-Aware Computer Systems, PACS 2003, held in San Diego, CA, USA in December 2003.The 14 revised full papers presented were carefully selected during two rounds of reviewing and improvement from 43 submissions. The papers span a wide spectrum of topics in power-aware systems; they are organized in topical sections on compilers, embedded systems, microarchitectures, and cache and memory systems.