In American law, the three types of contracts are express contracts, implied contracts, and quasi-contracts. The difference is how each one forms: an express contract spells out its terms in spoken or written words, an implied contract arises from the way the parties behave, and a quasi-contract is imposed by a court to prevent one party from unfairly benefiting at another’s expense, even when no real agreement existed.1Legal Information Institute. Contract
All three can create enforceable obligations. What changes from one to the next is what a court looks at to decide whether an obligation exists in the first place.
Express Contracts
An express contract is one where the parties state their terms directly. Nobody has to guess what was agreed to. A signed apartment lease that lays out the rent, the move-in date, and maintenance responsibilities is an express contract. So is a written employment agreement covering salary, duties, and how either side can end the relationship. Because the terms are visible from the start, these contracts are the easiest to enforce when something goes wrong.
Verbal agreements count as express contracts too, as long as the terms are clear and both parties understand them.2Investopedia. Oral Contracts: Definitive Guide to Proving and Enforcing Agreements If you tell your neighbor you will pay her $50 to mow your lawn by Saturday and she agrees, that is an enforceable express contract. The catch is proof. Written contracts come with a built-in paper trail. Oral contracts rely on memory and whatever secondary evidence exists, such as text messages, emails, or a witness who overheard the conversation. If a dispute reaches court, the person claiming the contract existed carries the burden of proving its terms.
This is where follow-up documentation matters. Even a quick text after a handshake deal (“Just confirming: you’ll deliver the furniture by March 15 for $800”) can be the difference between a contract you can enforce and a he-said-she-said argument.
When an Oral Express Contract Isn’t Enough
Oral express contracts are legally valid, but not for everything. A rule called the Statute of Frauds requires certain categories of agreements to be in writing and signed by the party being held to the deal, or a court will generally refuse to enforce them.3Legal Information Institute. Statute of Frauds The categories that typically must be in writing include:
- Contracts to buy, sell, or transfer an interest in real estate.
- Agreements that cannot be fully performed within one year from the date they are made.
- Contracts for the sale of goods priced at $500 or more, under the Uniform Commercial Code.
- Promises to pay someone else’s debt.
State laws vary on additional categories and specific thresholds, so a contract that is enforceable without writing in one state may not be in another. The underlying principle is the same everywhere: for high-stakes or long-duration agreements, the law wants something more reliable than memory.
Implied Contracts
An implied contract forms not from spoken or written words but from the way people behave. The legal term is “implied-in-fact,” and it means a court looks at the circumstances and concludes both parties acted as though they had an agreement, even if neither one said so explicitly.4Legal Information Institute. Contract Implied in Fact The key ingredient is mutual intent: both sides have to act in a way that signals they understand an obligation exists.
Everyday life is full of these. When you sit down at a restaurant and order a meal, you have not signed anything, but your conduct creates a binding agreement: the restaurant will serve the food, and you will pay the listed price. The same logic applies when you sit in a barber’s chair and accept a haircut, or when you hand your car keys to a valet. Nobody recites terms. The situation makes the terms obvious.
Implied Contracts at Work
One place implied contracts surprise people is employment. Most jobs in the United States are “at-will,” meaning either side can end the relationship at any time for almost any reason. But an employer’s own actions can quietly override that default. If a company handbook says employees will only be fired “for cause,” or if management consistently follows a progressive discipline process before terminating anyone, a court may find that those practices created an implied contract limiting the employer’s ability to fire at will.5Legal Information Institute. Employment-At-Will Doctrine
Employers who want to preserve at-will flexibility typically include clear disclaimers in their handbooks and avoid language that sounds like a guarantee of continued employment. Inconsistent enforcement is the real danger. Even a well-drafted handbook loses its protective effect if managers routinely ignore its procedures, because those patterns of behavior become the implied terms a court actually enforces.4Legal Information Institute. Contract Implied in Fact
Quasi-Contracts
A quasi-contract is not really a contract at all. It is a legal fiction courts use to prevent one person from unfairly profiting at another’s expense. The formal name is “implied-in-law contract” or “constructive contract,” and unlike the first two types, it does not require any mutual agreement or intention to be bound.6Legal Information Institute. Quasi Contract A court simply decides that fairness demands one party compensate the other.
A classic scenario: a delivery driver drops off building materials at your house by mistake, and you use them to finish a deck. You never ordered the materials and never agreed to pay for them, but you benefited from them. A court can impose a quasi-contract requiring you to pay their value. Another common example is emergency medical care. A doctor treats an unconscious accident victim who obviously cannot consent to treatment. The law implies an obligation to pay for those services, because allowing the patient to receive life-saving care for free would unjustly enrich them.
Proving Unjust Enrichment
To win a quasi-contract claim, the person seeking payment generally has to show three things: that they conferred a benefit on the other party, that the other party knew about or appreciated the benefit, and that letting them keep it without paying would be unfair. Courts call this “unjust enrichment,” and the remedy is restitution, meaning the enriched party pays back the reasonable value of whatever they received. The amount is not based on a contract price, since no contract exists, but on what the benefit was actually worth.
How to Tell Which Type You Are Dealing With
The quickest way to place a situation into the right category is to ask where the terms came from.
- If both sides said or wrote the terms, it is an express contract.
- If neither side spelled anything out but both acted as though a deal was in place, it is an implied contract.
- If one side received a benefit without any agreement at all and fairness calls for payment, it may support a quasi-contract claim.
The same underlying transaction can shift from one category to another depending on what the parties did. A verbal “I’ll pay you to paint my fence” is express. Letting a painter you have hired every spring show up and start work without discussing it this time is implied. A painter who shows up at the wrong house and paints the fence of a stranger who watches and says nothing is a quasi-contract problem. The facts determine the category, and the category determines what a court will look at to decide whether anyone owes anyone else.