This book constitutes the refereed proceedings of the 11th International Colloquium on Structural Information and Communication Complexity, SIROCCO 2004, held in Smolenice Castle, Slowakia in June 2004.The 26 revised full papers presented were carefully reviewed and selected from 56 submissions. Among the topics addressed are WDM networks, optical networks, ad-hoc networking, computational graph theory, graph algorithms, radio networks, routing, shortest-path problems, searching, labelling, distributed algorithms, communication networks, approximation algorithms, wireless networks, scheduling, NP completeness, Byzantine environments