What is the legal doctrine for interpreting ambiguous contract terms against the drafter?

The doctrine for interpreting an ambiguous contract term against its drafter is contra proferentem.

The Latin phrase means roughly “against the offeror” or “against the proposer.” It reflects the idea that the party who chose the wording should bear the risk when the language remains genuinely unclear. Courts often connect the rule to fairness, especially when one party supplied a standard-form or adhesion contract and the other had little opportunity to negotiate.

Contra proferentem is usually a rule of last resort, not the first step in contract interpretation. A court normally examines the text, the agreement as a whole, the parties’ conduct, and admissible surrounding evidence before turning to the anti-drafter presumption.

The doctrine is not universal in every application. Sophisticated parties may negotiate around it, statutes or specialized rules may control, and federal law can limit its use in particular settings. In Lamps Plus v. Varela, decided in 2019, the Supreme Court rejected using the rule alone to infer consent to class arbitration.