The term "systems engineering" is used to define a systematic way to undertake projects. There is much theory about the use of systems engineering, which from the speaker's experience has not been well applied to rail projects. The talk considers a major rail project, the East London Line Project, which is now under construction. In particular, the application of the principles of system engineering in a practical and pragmatic manner during the project definition phase is discussed, and how this will be taken forward through the delivery phase into public service.