In 1901 the Ongevallenwet, the first act regulating the insurance of workers in cases of accidents, was introduced in the Netherlands. In the historiography of the welfare state, introductions of acts like the Ongevallenwet mark a moment in time in which the collective started to take care of individual misfortune. This new form of state funded compensation for the loss of income due to disabilities came with a pressing individual responsibility to not misuse this social security arrangement. The regulations have constantly been tightened to make sure ‘the right people’ receive benefits. But when was a person truly incapable to work? Social security legislation necessitated classification. As philosophers of science have shown, classifications are moving targets that interact with our investigations. Interaction with the classification therefore ‘makes up’ the label that is being described. In line with these insights, this research examines the search for identifying properties of incapacity to work as a process of making up incapacity to work. This dissertation provides a fresh look at the ways in which incapacity for work has historically been produced. It analyses the actions and practices that have created and sustained the phenomenon of incapacity for work. It examines how it was enacted not only through the Ongevallenwet, but also through the interactions between the officials who implemented policies, the medical experts who testified about the nature, veracity and severity of the incapacity for work, and the individuals whose working capacity was under scrutiny. This research has shown how the three actors enacted incapacity for work in different ways, taking into account their position, knowledge, interests, (professional) rationalisations and values. Each actor undertook its own situated search for the properties of incapacity, resulting in a variety of realities of incapacity. Each assessment, however, required mediation, navigation and negotiation between legal frameworks, values and interests. Each ...