Offer and acceptance are two essential elements required to form an enforceable contract. An offer is made when one party makes a promise to do or refrain from doing some specified act in the future. And an acceptance occurs when an offer is accepted unequivocally—without conditions or ambiguity.

In other words, the acceptance must mirror the terms of the offer. If the acceptance varies from the terms of the offer it is considered a rejection of the offer and a counteroffer.

Acceptance may be expressed through words, deeds, or the performance called for in the contract.

In Washington State, as in other jurisdictions, the concepts of offer and acceptance are fundamental to the formation of a legally binding contract. An offer is a clear proposal made by one party (the offeror) to another (the offeree), indicating a willingness to enter into a contract on certain terms. Acceptance, on the other hand, must be an unequivocal agreement to those terms. It can be communicated through words, actions, or performance, as long as it is in line with the terms of the offer. If the acceptance adds new terms or changes the terms of the offer, it does not constitute a valid acceptance but rather a counteroffer, which the original offeror can then accept or reject. This principle is rooted in the common law of contracts and is consistent with the Uniform Commercial Code (UCC) as adopted in Washington, which governs the sale of goods. It's important to note that specific situations or types of contracts may have additional requirements or variations under Washington law.