This paper tackles an intellectual property theory that many scholars regard as fundamental to future policy debates over the scope of trademark protection: the trademark use theory. We argue that trademark use theory is flawed and should be rejected. The adoption of trademark use theory has immediate practical implications for disputes about the use of trademarks in online advertising, merchandising, and product design, and has long-term consequences for other trademark generally. We critique the theory both descriptively and prescriptively. We argue that trademark use theory over-extends the search costs rationale for the trademark system, and that it unhelpfully elevates formalism over contextual analysis in trademark law rule...