The two-volume set, LNCS 9878 and 9879 constitutes the refereed proceedings of the 21st European Symposium on Research in Computer Security, ESORICS 2016, held in Heraklion, Greece, in September 2016. The 60 revised full papers presented were carefully reviewed and selected from 285 submissions. The papers cover a wide range of topics in security and privacy, including data protection: systems security, network security, access control, authentication, and security in such emerging areas as cloud computing, cyber-physical systems, and the Internet of Things.