The thesis is concerned with the study and reliability analysis of signalling systems of Indian Railways (IR). The research work, reported in this thesis, has been carried out to address a few operation- and technology-related critical issues of railway signalling systems. In particular, the research work, with reference to railway signalling systems, has been specifically directed (i) to model its interacting variables, parameters, and physical components in different scenarios and conditions, (ii) to analyze the causes of failures of different components and their effects on signalling performance, and (iii) to find out an appropriate methodology for its reliability analysis. The working principles of railway signalling systems are very complex in nature. A signalling system is represented in terms of several types of working components and variables, such as panel, cable, relay, ‘point-and-point machine’, ‘track circuit’, back indication, ‘signal-unit’, point-drive and signal-drive cards, power supply, and level crossing gate, in all there possible combinations. There exists 31 such combinations in IR signalling systems. In order to measure and evaluate reliability under different situations, it has to be generically represented in terms of types of interlocking, number of tracks, types of approaching and departure signals, and signalling routes in all possible combinations.