This book constitutes the refereed proceedings of the Third International Conference on Generative Programming and Component Engineering, GPCE 2004, held in Vancouver, Canada in October 2004. The 25 revised full papers presented together with abstracts of 2 invited talks were carefully reviewed and selected from 75 submissions. The papers are organized in topical sections on aspect-orientation, staged programming, types for meta-programming, meta-programming, model-driven approaches, product lines, and domain-specific languages and generation.