This publication provides guidance and recommendations to nuclear organizations by offering a practical approach to assessing the behavioural competencies for safe, secure and effective performance across the nuclear workforce. It outlines a variety of tools and approaches that can aid the behavioural assessment processes and provides both general and role-specific recommendations to improve the quality of selection, promotion, training and development decisions. Also addressed in the publication are challenges, key issues and critical considerations for assessment practices. This guidance can be used by Member States as a foundation upon which to develop or improve a comprehensive behavioural competency assessment programme and contribute to building a sustainable nuclear workforce comprised of high performing nuclear professionals.