The concept of biocapitalism emerged within debates on global bio-industries, including reproduction industries, and the political project of a ‘bioeconomy’ that the OECD advocates since the mid-2000s. ‘Biocapitalism’ refers to processes of the primary valorization of materials derived from human bodies and nonhuman living beings, to the meaning of these processes for capitalist accumulation strategies and to related transformations of modes of labour, exploitation and subjectivation. Although the realities and prospects of biocapitalism make it necessary to go beyond Marx’ critique of political economy and to include analyses of gender relations, the (post)colonial situation, 21st-century biopolitics, and human-nature relations, Marx’ theory of capitalism provides crucial insights on which a critical theory of biocapitalism can build. In particular, Marx’ analysis of the commodity-form, his concept of labour, the theory of primitive accumulation, and his analysis of the ground-rent are widely discussed with respect to biocapitalism. Basically, a critical theory of biocapitalism needs to explain how it is possible that materials such as egg-cells, sperm or organic tissue circulate as disposable things. Although these ‘things’ must, to a large extent, be conceived of as proto-commodities rather than as commodities proper because their exchange is rarely fully monetized, Marx’ critique of commodity fetishism is instructive. It reveals that an analysis and critique of biocapitalism should not focus on the ‘things’ in question – their specific biological properties, respectively their naturalness or artificiality. In contrast, what needs to be scrutinized are the social practices and relations through which body materials come to function as commodities or proto-commodities, and that constitute subjects as proprietors of their bodies and body materials. To a large extent the difficulties that a critical theory of biocapitalism faces result from the fact that primary valorization refers to materials and processes which do not exist in unmediated ways but which are made accessible or generated only through techno-scientific procedures, and thus knowledge production and technological intervention. Because biocapitalism refers to organic or sub-organic materials and processes, analyses of biocapitalism are frequently shaped by a vitalist vocabulary. In order to translate this vocabulary into a critical social theory, and to make clear that what is at stake is not ‘life itself’ but historically specific practices and relations, it is helpful to refer to Marx’ vocabulary of political economy. According to Christian Zeller, Kean Birch and David Tyfield, Marx’ analysis of ground-rent provides a model for understanding how, in biocapitalism, rent is derived from knowledge which is enclosed as intellectual property. Other scholars draw a comparison between biocapitalist primary valorization and Marx’ analysis of the process of primitive accumulation. Following Marx and Rosa Luxemburg, the constitution of new biocapitalitst resources and (proto-)commodities can be understood as new enclosures and as another extension of capitalist accumulation to its non-capitalist milieu. Melinda Cooper and Catherine Waldby stress that this extension entails qualitative modifications, namely an “experimental intervention into the temporality of living matter” and an “active shaping of the body through scientific technologies” (Cooper & Waldby 2015, 94). Indeed, the enclosure of common land in 17th-century England, too, not only constituted private property but transformed society at large and modes of existence, including body and nature relations. Not least, primitive accumulation, broadly conceived, included the shaping of the labouring subject, or of individuals that conceive of themselves as proprietors of a potential called ‘labour power’. Neither ‘labour’ nor ‘labour power’ are thus universal concepts, as Marx highlights in the Introduction to the Grundrisse from 1857, but belong to bourgeois society. This insight should be kept in mind if the concept of labour is used to politically articulate biocapitalist relations of exchange as exploitation. Although it certainly makes sense to argue that monetized or semi-monetized practices such as surrogacy, egg cell and tissue ‘donation’, or participation in clinical trials should be regulated through labour legislation in order to guarantee some legal protection, Marx’ analysis of wage labour opens up another perspective: the transformation of social relations that rely on the appropriation of foreign labour power. A critique of biocapitalism thus has to do more than claim legal protection of labour, body, and nature. It needs to scrutinize all social relations that account for the production, circulation and consumption of bio-materials. Accordingly, a critical theory of biocapitalism cannot restrict itself to an accumulation-centred analysis of capitalism but needs to understand (bio-)capitalism as social formation that integrates monetized and non-monetized economic forms, multiple forms of power and domination, and re-shapes subjectivities, needs and desires. In addition, it re-shapes body politics and human-nature-relations and constitutes new forms of extractivism. Certainly, a critical theory of biocapitalism – which still needs to be formulated – has to renounce the double temptation of techno-determinism and economism, but it can get much inspiration from the praxeological aspects of Marx’ thought.