Direct disability assessment within social security is not just theoretically desirable, but can be implemented in practice. We have shown that there are three distinct ways that this can be done, each with different strengths and weaknesses. Further research is needed to clarify the costs, validity/legitimacy, and consequences of these different models. Implications for rehabilitation It has recently been argued that social security disability assessments should directly assess work capacity rather than simply assessing functioning - but we have no understanding about how this can be done in practice. Based on case studies of nine countries, we show that direct disability assessment can be implemented, and argue that there are three different ways of doing it. These are "demonstrated assessment" (using claimants' experiences in the labour market), "structured assessment" (matching functional requirements to workplace demands), and "expert assessment" (the judgement of skilled professionals). While it is possible to implement a direct assessment of work capacity for social security benefits, further research is necessary to understand how best to maximise validity, legitimacy, and cost-effectiveness.