This book covers the fundamental concepts of reliability theory, including key reliability metrics and the analytical relationships between them. It explores issues related to the reliability of software and hardware systems, introduces the principles of recovery theory, and examines the reliability of both repairable and non-repairable technical devices. The text discusses structural reliability schemes and methods for assessing the reliability of hardware-software complexes, taking into account the characteristics of software and information systems. Additionally, it presents practical techniques for statistical reliability evaluation. Designed for fourth-year full-time students and fifth-year part-time students specializing in Information Systems and Technologies (Program 230201), this book provides essential knowledge for understanding and analyzing system reliability.