This article contrasts two understandings of labour law and its relationship with the labour market, a “naturalistic” understanding that sees the labour market as a “natural” sphere of free economic activity, and a “constitutive” understanding that sees markets as constituted by legal and other institutional processes. While the former sees labour law as an “interference” in an efficient system and a “restriction” on an innate freedom to contract, the latter suggests that labour law plays an integral part in ensuring the market’s efficient and sustainable functioning. The article goes on to explore how these understandings affect legal doctrine, with a particular focus on how questions of employment status are addressed. Taking the concept of “mutuality of obligation” as a focal point, it shows that a “naturalistic” understanding of labour law pervades contemporary policy-debates and juridical discussions of employment status. The cost of naturalising employment status in this way is a loss of clarity in the tests for identifying the employment relationship and hence a loss of regulatory effectiveness for labour law.