State fragility has become a resonant term in the development discourse over the past decade. In its early days it served as a catch-all phrase used by donor organisations to draw attention to the need to assist ‘fragile states’. In response to the call for a better understanding of how to deal with these countries, there was a surge in measures of fragility. However, it was not long before academics pointed to the murkiness and fuzziness of the term, and identified several caveats to most of the proposals for quantification. This paper reviews existing approaches to operationalise this concept, distinguishing between those that offer no ranking or only partial rankings of fragile states, and those providing ordinal lists of countries. The examination of their theoretical underpinnings lends support to the critical view that most existing approaches are undermined by a lack of solid theoretical foundations, which leads to confusion between causes, symptoms and outcomes of state fragility.