This book constitutes the refereed proceedings of the 18th International Conference on Information Security, ISSA 2019, held in Johannesburg, South Africa, in August 2019.The 12 revised full papers presented were carefully reviewed and selected from 35 submissions. The papers are dealing with topics such as authentication; access control; digital (cyber) forensics; cyber security; mobile and wireless security; privacy-preserving protocols; authorization; trust frameworks; security requirements; formal security models; malware and its mitigation; intrusion detection systems; social engineering; operating systems security; browser security; denial-of-service attacks; vulnerability management; file system security; firewalls; Web protocol security; digital rights management; distributed systems security.