This book constitutes the proceedings of the 20th IFIP WG 11.12 International Symposium on Human Aspects of Information Security and Assurance, HAISA 2026, held in Orebro, Sweden, during July 6–8, 2026.The 36 full papers included in this book were carefully reviewed and selected from 49 submissions. They were organized in topical sections as follows: Awareness & Education; Social Engineering; Culture; Management, Policy and Skills; Technical Attacks & Defenses.