This volume constitutes the thoroughly refereed post-conference proceedings of the 9th International Conference on Verified Software: Theories, Tools, and Experiments, VSTTE 2017, held in Heidelberg, Germany, in July 2017. The 12 full papers presented were carefully revised and selected from 20 submissions. The papers describe large-scale verification efforts that involve collaboration, theory unification, tool integration, and formalized domain knowledge as well as novel experiments and case studies evaluating verification techniques and technologies.