This publication serves as a high-level introduction to systems engineering for instrumentation and control at nuclear facilities. Systems engineering is a holistic, interdisciplinary and cooperative approach to the engineering of large and complex systems. Many industrial sectors consider the approach as a necessary means to develop and utilize current and fit-for-purpose systems. This publication is intended to assist Member States in understanding the philosophy and methodologies of systems engineering as presented by the ISO/IEC/IEEE 15288 standard, and provide guiding principles for the application of systems engineering to nuclear facilities and their instrumentation and control. Where necessary, it provides relevant referrals to other publications for detailed practical aspects.