This book constitutes the refereed proceedings of the 19th International Conference on Computer Networks, CN 2012, held in Szczyrk, Poland, in June 2012. The 48 revised full papers presented were carefully reviewed and selected for inclusion in the book. The papers address subjects such as new and emerging technologies related to networking fields; fundamentals of computer networks; internet and internetworking; security and safety issues; industrial computer networks; wireless systems and sensor networks; the theory of queues and queuing networks; applications and computer networks usage.