What contribution can nuclear energy make to improve the security of energy supply? This study, which examines a selection of OECD member countries, qualitatively and quantitatively validates the often intuitive assumption that, as a largely domestic source of electricity with stable costs and no greenhouse gas emissions during production, nuclear energy can make a positive contribution. Following an analysis of the meaning and context of security of supply, the study uses transparent and policy-relevant indicators to show that, together with improvements in energy efficiency, nuclear energy has indeed contributed significantly to enhanced energy supply security in OECD countries over the past 40 years.