A contract is an agreement that creates obligations enforceable by law. Whether a particular deal qualifies depends on its terms, the parties’ words and conduct, required formalities, defenses and the law governing the transaction.

A signed page is not automatically enforceable, and a handshake is not automatically meaningless. Separate three questions: Was a contract formed? Can its terms be proved? Does a writing rule or another legal limitation prevent enforcement? This U.S. overview uses California and federal examples; rules vary by state, subject matter and country.

What makes a contract legally enforceable?

California’s 2026 civil jury instructions, particularly CACI 302, illustrate the formation inquiry: sufficiently clear terms, an exchange of value and agreement shown through outward words and conduct. Capacity and lawful purpose also matter. These are related questions, rather than a rule that every jurisdiction counts precisely the same number of elements.

Offer and acceptance: a negotiation is not necessarily an offer. The communication must indicate terms on which acceptance would create the bargain. A reply proposing a change may require further agreement; the result depends on the governing rules. CACI 307 and 309 address those formation issues in California.

Exchange does not mean cash only. Consideration may include a promise to perform work or give up a permitted action. A purely generous promise does not by itself establish the exchange needed for an ordinary bargain. Exceptions and other legal doctrines require their own analysis.

Contract, agreement or promise?

The heading on the document does not decide the result. Calling a page an “agreement,” a “proposal” or a “contract” cannot replace an analysis of what the parties actually communicated and accepted.

A five-question contract test

This screening checklist is not a court ruling or individualized legal advice.

1. Who agreed to what? Identify the actual parties, offered terms, acceptance and whether a person acting for a business had authority.
2. What was exchanged? Identify each side’s promised benefit, performance or restraint rather than assuming every promise is a bargain.
3. Are the obligations sufficiently clear? Find the subject matter, payment method, performance and relevant timing; distinguish an agreed term from something left for negotiation.
4. Can these parties lawfully make this deal? Check capacity, lawful purpose and possible consent problems such as fraud or duress. A signature does not settle those questions.
5. What formalities and evidence are required? Check the transaction’s writing and signature rules, the applicable state law and the evidence of agreement. A contract can face a proof problem even when the type of deal does not require writing.

Two practical examples

Stronger formation evidence: a defined service. A freelance editor offers to edit a specified report for $300 by Friday. The customer replies accepting those terms, and both keep the messages. Assuming the other legal requirements are met, the agreed work, payment and acceptance provide a clearer basis for a contract than an unresolved conversation. The messages are evidence; they do not automatically eliminate capacity, authority or other defenses.

Weaker formation evidence: a possible gift. A friend says, “I might give you my old bicycle when I replace it,” and nothing is promised in exchange. That wording does not show the same definite commitment or bargained exchange. Do not treat every disappointment as a contract breach, or assume this example resolves a separate reliance-based claim.

Do contracts have to be in writing?

Not all do. California Civil Code §§ 1619–1624 recognizes express and implied contracts and generally permits oral contracts except where a statute requires writing. CACI 304–306 also distinguish oral terms, agreement inferred from conduct and a deal awaiting a formal document. Whether the parties intended to be bound before signing can be decisive.

A statute of frauds is a writing requirement for specified transactions, not a rule that all unwritten agreements are fraudulent. California § 1624 includes, among other categories, certain real-property transactions, promises answering for another’s debt and agreements that by their terms cannot be performed within a year of making them. The exact category, exceptions and required signature matter.

Goods have a separate example: California Commercial Code § 2201, corresponding to UCC § 2-201, generally requires a sufficient signed record for goods priced at $500 or more, subject to its exceptions. The section addresses merchant confirmations, specially manufactured goods, court admissions and accepted payment or goods in specified circumstances. This is not a $500 rule for all services or every jurisdiction, and partial performance is not a universal cure for missing writing.

Electronic agreements: the federal E-SIGN Act, 15 U.S.C. § 7001, generally prevents denying legal effect solely because a covered interstate or foreign-commerce transaction uses an electronic record or signature. It preserves other legal requirements, has consumer-disclosure provisions and operates with statutory exceptions. An electronic signature does not validate an otherwise unlawful or unagreed transaction.

Oral contracts: enforceable versus provable

If the transaction may be oral, proving the actual agreement remains a separate problem. Preserve existing evidence that identifies the terms, parties and conduct:

• Emails or texts showing the proposal, acceptance and changes, with the complete conversation rather than isolated lines.
• Quotes, purchase orders, invoices and payment records, checking which terms were actually accepted.
• Evidence of requested work, delivery or other performance and how the recipient responded.
• Witnesses who heard the actual exchange and admissions already made by the parties.
• Any signed document and the version in effect when the parties agreed.

An invoice sent afterward does not by itself prove the other side accepted every printed term. Evidence of performance may help prove agreement, but does not automatically satisfy a statute of frauds. Where terms remain unclear, seek a clear written record promptly rather than treating your own recollection as conclusive.

What happens when a contract is breached?

A breach is a failure to perform an obligation without a legally sufficient excuse, or doing what the contract prohibits. A claim for Damages requires more than saying someone broke a promise: identify the contract, required performance, the breach and resulting harm, with any conditions or excuses addressed.

CACI 303 and 350 illustrate California’s inquiry into performance, breach, causation and compensation. Compensatory damages aim to compensate for the legally recoverable harm; they are not automatically whatever amount a claimant demands. Keep records of the loss and the connection to the breach. The remedy and any limits depend on the transaction and applicable law.

Specific performance asks a court to require the promised act rather than merely award money. California’s specific-performance statutes illustrate both availability and limits, including restrictions involving personal services and insufficiently certain obligations. Having a contract does not guarantee an order forcing performance.

Common contract types

• Express: the agreement’s terms are stated in spoken or written words.
• Implied in fact: agreement is established from the parties’ conduct and circumstances, rather than an express statement of every term.
• Bilateral: the bargain exchanges promises, such as a promise to provide services for a promise to pay.
• Unilateral: an offer invites acceptance through specified performance, such as completing the act described in a reward offer. The offer’s actual terms and applicable rules determine formation.

These descriptions can overlap. “Oral” does not mean “implied,” and “written” does not mean “bilateral.”

Frequently asked questions

Can a handshake be binding?

Possibly, if the applicable formation requirements are met and no writing rule prevents enforcement. Establish what was actually agreed and how you can prove it; a handshake alone does not answer those questions.

Does every contract need signatures?

No universal signature rule covers every deal. Some transactions require a signed record, and parties may make signing a condition of being bound. Check both the governing law and the agreement.

Is every promise a contract?

No. An ordinary bargain requires more than a statement of future intention. Check assent, exchange, definite obligations and the other applicable requirements. A separate legal doctrine may require different analysis.

Can I cancel after agreeing?

Do not assume a general right to cancel merely because you changed your mind. Review termination provisions, any transaction-specific statutory cancellation rights and possible defenses. Preserve the records and obtain advice promptly if a notice period or disputed obligation is involved.

Primary authorities checked October 19, 2026. California jury instructions are the official 2026 edition; federal Code pages reflect the official temporary edition through Public Law 119-121, October 9, 2026. Identify the governing law and transaction before relying on a general contract checklist.