This book constitutes the refereed proceedings of the 9th International Symposium on Engineering Secure Software and Systems, ESSoS 2017, held in Bonn,  Germany in July 2017. The 12 full papers presented together with 3 short papers were carefully reviewed and selected from 32 submissions. 
The goal of this symposium is to bring together researchers and practitioners to advance the states of the art and practice in secure software engineering.