This article asks a simple question: when indistinguishable items of personal property owned by A and by B are mixed together, what rights do A and B have in relation to the resultant mass? It is argued that there is insufficient evidence in the positive law to provide any convincing answer to this question, and so it is asked which interpretation that can be drawn out from the law ought to be adopted. It will be shown that – both in relation to mixtures of goods and mixtures of cash – a rule of co‐ownership is to be preferred. [---]