What makes a contract legally binding?
A signature alone doesn't create a contract. US law requires a handful of elements to be present before an agreement is enforceable — here's each one.
Formation, not signature
People often assume a contract becomes binding the moment it's signed. In reality, enforceability depends on how the agreement was formed. US contract law looks for a specific set of elements — offer, acceptance, consideration, capacity, and a lawful purpose. Signing matters, but it evidences agreement rather than creating it. (Whether an electronic signature counts is a separate question, covered in our e-signature law guide.)
1. Offer and acceptance
One party must make a clear offer, and the other must accept it on those terms — the classic “meeting of the minds.” An offer must be definite enough that a court could enforce it. A response that changes the terms is a counter-offer, not acceptance, and restarts the process. Ambiguity here is the most common reason informal deals fall apart.
2. Consideration
Each side must exchange something of value — money, goods, services, or a promise to do (or refrain from doing) something. Consideration is what separates a contract from a gift promise, which generally isn't enforceable. The value doesn't have to be equal, but it must be real: a purely symbolic exchange may not suffice.
3. Capacity and lawful purpose
The parties must have legal capacity to contract — typically meaning they're adults of sound mind and, for a business, that the signer is authorized to bind the entity. The contract's purpose must also be lawful; agreements to do something illegal are unenforceable. Some contracts additionally must be in writing under the Statute of Frauds, such as real-estate sales and agreements that can't be performed within one year.
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Frequently asked questions
Does a contract have to be in writing?
Not always — many oral contracts are enforceable. But certain types must be written under the Statute of Frauds, including real-estate transfers and agreements lasting more than a year. Writing is always safer because it proves the terms.
Is a signature required for a contract to be binding?
Not strictly. A contract can form through conduct or oral agreement. A signature is powerful evidence of assent, which is why written and signed contracts are the norm.
What is consideration in simple terms?
It's the value each side gives up. If only one party promises something and gets nothing back, it's usually an unenforceable gift promise rather than a contract.