This book constitutes the proceedings of the 9th International Symposium on Cyberspace Safety and Security, CSS 2017, held in Xi'an, China in October 2017. The 31 full papers and 10 short papers presented in this volume were carefully reviewed and selected from 120 submissions. The papers focus on cyberspace safety and security such as authentication, access control, availability, integrity, privacy, confidentiality, dependability and sustainability issues of cyberspace.