This book constitutes the refereed post-conference proceedings of the 25th International Colloquium on Structural Information and Communication Complexity, SIROCCO 2018, held in Ma'ale HaHamisha, Israel, in June 2018. The 23 full papers and 8 short papers presented were carefully reviewed and selected from 47 submissions. They are devoted to the study of the interplay between structural knowledge, communications, and computing in decentralized systems of multiple communicating entities and cover a large range of topics.