This book constitutes the refereed proceedings of the 20th International Conference on Information Systems Security, ICISS 2024, held in Jaipur, India, during December 16-20, 2024. The 18 full papers and 6 short papers included in this book were carefully reviewed and selected from 93 submissions. They were organized in topical sections as follows: System Security; Network Security; Attack; Malware and Vulnerability Detection; Privacy & Usability; AI Security; and Industry Demo/Practice.