With the post-industrialization and flexibilization of European labour markets, research on social and economic correlates of labour market vulnerability and weak labour market attachment is growing. Part of this literature conceptualizes these correlates in terms of dualization and insider–outsider divides in an attempt to explore their political implications: this article is written in order to contribute to this strand of research. In this article, we propose a conceptualization and measurement of labour market insiders and outsiders, based on their respective risk of being atypically employed or unemployed. We propose both a dichotomous measure of insiders/outsiders and a continuous measure of the degree of an individual’s ‘outsiderness’. We argue that such risk-based measures are particularly suited for research on the policy preferences and political implications of insider–outsider divides. On the basis of EU-SILC and national household panel data, we provide a map of dualization across different countries and welfare regimes. We then explore the correlates of labour market vulnerability – that is, outsiderness – by relating it to indicators of income and upward job mobility, as well as labour market policy preferences. The results consistently confirm an impact of labour market vulnerability, indicating a potential for a politicization of the insider/outsider conflict.