This two-volume set, LNCS 16908-16909, 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 66 full papers included in these volumes were carefully reviewed and selected from 297 submissions. The papers cover the following topical sections: Part I: Collective Intelligence and Collective Decision-Making; Quantum for Collective; Collective Intelligence in Deep Learning Techniques; Natural Language Processing; and Collective Intelligence in Data Mining and Machine Learning; Part II: Social Networks and Intelligent Systems; Cybersecurity and Internet of Things; Computational Intelligence for Digital Content Understanding; Computational Intelligence in Medical Applications; and Knowledge Engineering and Application for Industry 4.0.