This book constitutes the refereed proceedings of the 19th International Colloquium on Structural Information and Communication Complexity, SIROCCO 2012, held in Reykjavik, Iceland for 3 days starting June 30, 2012. The 28 revised full papers presented were carefully reviewed and selected from 54 submissions. SIROCCO is devoted to the study of communication and knowledge in distributed systems. Special emphasis is given to innovative approaches and fundamental understanding, in addition to efforts to optimize current designs. The typical areas include distributed computing, communication networks, game theory, parallel computing, social networks, mobile computing (including autonomous robots), peer to peer systems, communication complexity, fault tolerant graph theories, and randomized/probabilistic issues in networks.