This two-volume set CCIS 3043-3044 constitutes the refereed proceedings of the 18th International Conference on Computational Collective Intelligence, ICCCI 2026, held in Heraklion, Crete, Greece, during September 23–25, 2026.The 74 full papers included in this book were carefully reviewed and selected from 297 submissions. They were organized into the following topical sections:Part I: Collective Intelligence and Collective Decision-Making; Collective Intelligence in Deep Learning and Neural Architectures; Natural Language Processing and Speech Systems; Cybersecurity, IoT and Trustworthy Systems; and Collective Intelligence in Medical Imaging and Healthcare Applications.Part II: Collective Intelligence in Optimization and Swarm Systems; Collective Intelligence in Explainable AI; Collective Intelligence in Advanced Computing; Collective Intelligence in Human-Centered AI; and Applied Machine learning.