This book constitutes the refereed proceedings of the Third International Workshop on Algorithm Engineering, WAE'99, held in London, UK in July 1999.The 24 revised full papers presented were carefully reviewed and selected from a total of 46 submissions. The papers present original research results in all aspects of algorithm engineering including implementation, experimental testing, fine-tuning of discrete algorithms, development of repositories of software, methodological issues such as standards for empirical research on algorithms and data structures, and issues in the process of converting user requirements into efficient algorithmic solutions and implementations.