This book constitutes the refereed proceedings of the 13th International Conference on Software Engineering and Formal Methods, SEFM 2015, held in York, UK, in September 2015. The 17 full papers presented together with 2 invited and 6 short papers were carefully reviewed and selected from 96 submissions. The topics of interest included the following aspects of software engineering and formal methods: program verification, testing, certification, formal specification and proof, testing and model checking, planning, modelling, and model transformation.