In contract law, the “mirror image rule” is a doctrine stipulating that any acceptance of an offer is deemed to be an to be an unconditional assent to the terms of the offer exactly as it is, without any changes or modifications. Thus, at least historically, any acceptance to an offer had to embrace the pricing and any other information included in the offer as it was presented.
The mirror image rule no longer applies in contract cases that are governed by the Uniform Commercial Code (UCC), but it does still apply for non-UCC cases that instead follow common law. Under the Uniform Commercial Code, a clearly expressed acceptance can create a binding sales contract even if the acceptance contains added or different terms when compared to the offer. See UCC § 2-206(3).
[Last updated in July of 2023 by the Wex Definitions Team]