This book constitutes the thoroughly refereed post-proceedings of the Third International Workshop on Formal Approaches to Testing of Software, FATES 2003, held in Montreal, Quebec, Canada, on October 6th, 2003.

The 18 revised full papers presented were carefully selected from 43 submissions during two rounds of reviewing and improvement. The papers are organized in topical sections on program testing and analysis, test theory and test derivation algorithms, and test methods and test tools.