Reliability theory is presented as a science and academic discipline. Contains criteria, methods for the analysis and synthesis of technical and information systems, methods for ensuring and improving their reliability, scientific methods of operation. Non-recoverable and recoverable, non-redundant and redundant systems of long and short lifetime are considered. Methods for analyzing the reliability of technical and information systems under arbitrary laws of distribution of failure and recovery time are described. A number of methods previously unknown in reliability theory are proposed. For scientists, engineers, graduate students and technical students.