This paper provides a comprehensive discussion of the labour market security dimension of the OECD’s job quality framework, thereby complementing the analysis in Chapter 3 of the OECD Employment Outlook 2014 and Chapter 5 of the OECD Employment Outlook 2015. It makes three main contributions. First, it provides an in-depth discussion of the definition and measurement of labour market security. and discusses in detail the various methodological issues surrounding its measurement. Second, it offers a comprehensive statistical portrait of labour market security across countries, socio-economic groups and over time. Third, it investigates the statistical relationship between labour market insecurity and subjective measures of well-being. Importantly, we find that the risk of unemployment has a detrimental effect on the well-being of employed workers, and that this reflects to an important extent the risk of staying unemployed for a prolonged period of time. Policymakers should therefore focus not only on reducing the level of unemployment, but also on speeding up unemployment turnover at a given level of unemployment. Unemployment insurance also mitigates the adverse effect of unemployment risk, and particularly that of long-term unemployment, on the well-being of the employed.