Summary. Composite indicators are increasingly used for bench-marking countries’ performances. Yet doubts are often raised about the robustness of the resulting countries’ rankings and about the significance of the associated policy message. We propose the use of uncertainty analysis and sensitivity analysis to gain useful insights during the process of building composite indicators, including a contribution to the indicators’ definition of quality and an assessment of the reliability of countries’ rankings. We discuss to what extent the use of uncertainty and sensitivity analysis may increase transparency or make policy inference more defensible by applying the methodology to a known composite indicator: the United Nations's technology achievement index.