1. United Nations Convention on Contracts for the International Sale of Goods (CISG). (1980). Article 19(2). This article explicitly states, "a reply to an offer which purports to be an acceptance but contains additional or different terms which do not materially alter the terms of the offer constitutes an acceptance..." This is a direct rejection of the strict common law mirror image rule.
2. Schwenzer, I., & Hachem, P. (2012). The CISG—A Story of Worldwide Success. In I. Schwenzer & L. Spagnolo (Eds.), State of Play: The 3rd Annual MAA Schlechtriem CISG Conference (pp. 19-48). Eleven International Publishing. On page 30, the authors note that the CISG's approach in Article 19 "departs from the traditional 'mirror-image' rule known in many common law jurisdictions."
3. George Washington University Law School. (Courseware). Comparative Law: The Civil Law and Common Law Traditions. The course materials often highlight key distinctions in contract formation, noting that the civil law tradition's emphasis on good faith and the parties' intent leads to a less rigid formation process than the common law's mirror image rule.
4. National Contract Management Association (NCMA). (2019). Contract Management Body of Knowledge (CMBOK)®, 6th ed. Section 1.3.2, "Legal Systems." This section contrasts the codified nature of civil law with the precedent-based nature of common law, which is the source of doctrines like the mirror image rule. This foundational difference explains why such a rule is not a feature of civil law.