This book constitutes the refereed proceedings of the 33rd International Colloquium on Structural Information and Communication Complexity, SIROCCO 2026, held in Durham, UK, during June 9–11, 2026.

The 28 full papers included in this book were carefully reviewed and selected from 65 submissions.They focus on innovative methodological and solution approaches in structural knowledge, communication, and computing in decentralized systems of multiple comunicating entities.