This book constitutes the proceedings of the 17th International Conference on Information Technologies and Mathematical Modelling, ITMM 2018, named after A.F. Terpugov, and the 12th Workshop on Retrial Queues and Related Topics, held in Tomsk, Russia, in September 2018. The 30 papers presented in this volume were carefully reviewed and selected from 84 submissions. The conference covers various aspects of information technologies, focusing on queueing theory, stochastic processes, Markov processes, renewal theory, network performance equation and network protocols.