The book "Information Security" presents the refereed proceedings of the 18th International Conference on Information Security, ISC 2015, which took place in September 2015 in Trondheim, Norway. It includes 30 revised full texts selected from 103 submitted papers. The contributions cover a wide range of topics in the field of cryptography and cryptanalysis and are organized into various thematic sections. These sections include, among others, signatures, system and software security, block ciphers, protocols, network and cloud security, as well as fundamentals of encryption. The book is aimed at professionals and students who wish to engage with the latest developments and challenges in information security.