This book constitutes the proceedings of the 15th International Conference on Information Systems Security, ICISS 2019, held in Hyderabad, India, in December 2019. The 13 revised full papers and 4 short papers presented in this book together with 4 abstracts of invited talks were carefully reviewed and selected from 63 submissions. The papers cover topics such as: smart contracts; formal techniques; access control; machine learning; distributed systems; cryptography; online social networks; images and cryptography.