This thesis draws on the theory and method of social ontology to explore why labour law struggles to provide for wage security and clarity of employment status today. It starts by exploring at a conceptual level the relationship between law and capitalism, before moving on to engage more specifically with the concept of the wage, situating the analysis in a theory of the wage’s socio-economic function. The thesis understands the ‘wage’ as, initially, the market price of the commodity, ‘labour power’, which is exchanged in the labour market. As with any other ‘price’, the wage functions to coordinate decision making in the market. At the same time, however, the wage is also the cost of reproducing that commodity, a process which is not confined to the market but takes place in society more generally: this is the function of social reproduction. These two functions are not only conceptually and materially distinct; they are frequently in conflict. The price the market assigns to the labour commodity is not always, and not necessarily, that which is required to cover its costs of (re)production. The thesis shows that these functions of the wage find their expression in the various concepts the legal system uses to describe the payment made by employers to their workers. For example, the legal concept of the ‘wage’ corresponds closely to the economic idea of the wage as price, and the concept of ‘remuneration’ to the wage as the cost of social reproduction, shifting some of the social costs of employment onto the employer. How these conceptual tools are deployed, however, and thus how effectively these functions are performed in practice, depends on law’s own view of its ontological status: that is, the implicit position that the legal system takes on what constitutes ‘social reality’ beyond the text of a particular case or statute, and thus its view of whether, and to what extent, legal concepts can shape, as well as respond, to it. The thesis shows that whether the legal system sees its concepts playing an active role in constituting social and economic relations, or whether it sees them as passively reacting to the ‘demands’ of a ‘pre-constituted’ economic system makes a difference to the effectiveness of law in practice. Understanding law’s implicit ontology in this sense helps us to see why labour law struggles to provide for wage security and clarity of status. Thinking about law’s relationship with social reality can thus make an important contribution to our understanding of the problems of low pay and unclear employment status today.