This book constitutes the refereed proceedings of the 25th IFIP WG 6.1 International Conference on Testing Software and Systems, ICTSS 2013, held in Istanbul, Turkey, in November 2013. The 17 revised full papers presented together with 3 short papers were carefully selected from 68 submissions. The papers are organized in topical sections on model-based testing, testing timed and concurrent systems, test suite selection and effort estimation, tools and languages, and debugging.