This article looks back in history to understand how private debt developed into the kind of tradable asset, or commodity, that it is today. The article theorises that development, distinguishing in it three discrete but overlapping modes of commodification, namely propertification, impersonalisation and risk abstraction. The three modes shed light on changes in debt as a legal institution and in the economic and social functions of debt. Finally, the article shows that commodification of private debt is not just a phenomenon of the past, but something to be taken into account in future law-making, where the three modes of commodification may help to recognise particular opportunities and risks. This is illustrated by two actions included in the Commission's Capital Markets Union project, one regarding cross-border assignments of claims, the other the European securitisation market.