This book constitutes the proceedings of the Third International Symposium on Dependable Software Engineering: Theories, Tools, and Applications, SETTA 2017, held in Changsha, China, in October2017.The 19 full papers presented together with 3 invited talks  were carefully reviewed and selected from 31 submissions. The aim of the symposium is to bring together international researchers and practitioners in the field of software technology. Its focus is on probabilistic and statistical analysis; timed and hybrid systems; program analysis; modeling and verification; formalization; and tools.