UCC § 2-207
Additional Terms in Acceptance or Confirmation
(1) A definite and seasonable expression of acceptance or a written confirmation which is sent within a reasonable time operates as an acceptance even though it states terms additional to or different from those offered or agreed upon.
Professor's notes
Elements: (1) a definite and seasonable expression of acceptance operates as acceptance even if it states additional or different terms, unless acceptance is expressly conditional on assent to those terms; (2) the additional terms are proposals; between merchants they become part of the contract UNLESS the offer expressly limits acceptance, the additional terms materially alter, or objection is given; (3) conduct recognizing a contract is sufficient to establish one, and the terms are those on which the writings agree plus UCC gap-fillers (the knock-out rule).
Flender v. Tippins operationalizes the knock-out for conflicting forum clauses.
Common misunderstanding: students try to apply 2-207 like a flowchart and treat "additional" and "different" as synonyms. They are not. Most courts apply the knock-out only to "different" terms; "additional" terms run through subsection (2). The textual distinction does real doctrinal work.
Cases that operationalize this rule
Section 2-207 displaces the common-law mirror image rule for sales of goods. It recognizes that commercial parties often form contracts through exchanged forms that do not perfectly match. The provision’s complexity reflects an effort to preserve deals while allocating the legal effect of additional or different terms.