The law describing vendor's and purchaser's liens over personal property can only be described as baffling: there are cases to “prove” and “disprove” almost any proposition. This uncertainty is surprising. A contract of sale is one of the most basic forms of commercial activity, and an equitable lien would convert a vendor or purchaser into a secured creditor by operation of law. The advantages of such a position are self-evident, yet it remains unacceptably difficult to say when such advantages accrue. Fundamental equitable principles seem to support a simple analysis of vendor's and purchaser's liens which might eliminate some of the current uncertainties. This article describes that analysis. It concludes that one party to a sale contract has a lien over identified sale property whenever, and as soon as, all the contractual obligations assumed by that party have been carried out.