Effective requirements engineering and management are essential for modern nuclear instrumentation and control systems. This publication highlights the importance of effective requirements engineering and management for modern nuclear instrumentation and control systems. As digitalization and increasingly complex architectures evolve, precise and coherent requirements are essential to avoid misunderstandings that can compromise defence in depth, contribute to common cause failures, or lead to costly delays and performance issues. The publication provides Member States with practical guidance on requirements engineering and management philosophies, methodologies and implementation considerations, consistent with IAEA Safety Standards Series No. SSG-39, SSR-2/1 (Rev.1) and relevant Nuclear Security Series guidance. Designed to be regulatory agnostic, it presents generalized examples, good practices and lessons learned, without addressing the content of safety or security requirements already covered by existing standards.