This book constitutes the proceedings of the 18th International Conference on Information Technologies and Mathematical Modelling, ITMM 2019, named after A.F. Terpugov, held in Saratov, Russia, in June 2019. The 25 full papers presented in this volume were carefully reviewed and selected from 72 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.