The main types of agreements are oral, written, and implied agreements (grouped by how they are formed), unilateral and bilateral agreements (grouped by how obligations are structured), executory and executed agreements (grouped by status), and void and voidable agreements (grouped by enforceability). On top of these foundational categories, businesses and employers use specialized agreements like NDAs, non-competes, service level agreements, and force majeure clauses to handle specific risks. Which type applies to your situation depends on how the deal was made, what it covers, and what each side promised.
What Makes Any Agreement Legally Binding
Before the categories matter, every enforceable agreement needs four things: an offer and an acceptance on the same terms, consideration (an exchange of value), parties with legal capacity, and a lawful purpose. Miss one, and a court will likely refuse to enforce the deal.
Offer and acceptance means one side proposes clear terms and the other agrees to them without changes. A response that tweaks the price or adds conditions is a counteroffer, not an acceptance. Courts call the moment both sides understand and agree to the same obligations a “meeting of the minds.”
Consideration is what separates a binding agreement from a bare promise. Each side has to give up something or take on an obligation, usually money in exchange for goods or services, but it can also be a promise to do something or to refrain from doing something. Without it, a promise is treated as a gift and generally can’t be enforced.
Capacity generally means being at least 18 and mentally able to understand what you’re agreeing to. A contract signed by a minor is usually voidable at the minor’s option. Someone who was severely intoxicated or mentally incapacitated when they signed can also challenge the deal later. And the purpose has to be lawful. A contract to do something illegal is void from the start, no matter how carefully it was documented.
Oral Agreements
An oral agreement forms when parties reach a deal through spoken words rather than a signed document. These verbal commitments carry the same legal weight as written ones, as long as the basic elements are present. Most everyday transactions work this way. You agree on a price with a contractor over the phone, or you promise your neighbor you’ll mow their lawn for a set fee. Both are enforceable.
The challenge is proving an oral agreement exists. When a dispute arises, there’s no document to point to, so courts look at surrounding evidence: emails and texts that reference the deal, invoices or receipts showing payment, witness testimony, and how both parties behaved after the alleged agreement. Partial performance is especially persuasive. If you can show you delivered half the work and received half the payment, a court is far more likely to find a contract existed.
Oral agreements have hard limits. Certain categories of contracts must be in writing under a doctrine called the Statute of Frauds. If your deal falls into one of those categories, a handshake won’t hold up no matter how many witnesses heard it.
Written Agreements
Written agreements put the terms into a document both parties sign. The main advantage is clarity. Everyone can refer back to the same text when questions come up about deadlines, payment, or performance. For high-value transactions, writing isn’t just smart practice; it’s legally required.
When Writing Is Required: The Statute of Frauds
The Statute of Frauds is a rule adopted in every state that requires certain contracts to be in writing and signed. The categories vary slightly by state, but the most common include:
- Contracts for the sale of goods priced at $500 or more
- Contracts transferring an interest in real estate
- Agreements that cannot be completed within one year
- Promises to pay someone else’s debt
- Contracts made in consideration of marriage
For sales of goods, the Uniform Commercial Code sets the writing threshold at $500 or more.1Legal Information Institute. Uniform Commercial Code 2-201 – Formal Requirements Statute of Frauds The writing doesn’t have to be a formal contract. A signed memo, email, or invoice can satisfy the requirement as long as it shows a deal was made and identifies the key terms.
Electronic Signatures
A signature doesn’t have to be ink on paper. Under the Electronic Signatures in Global and National Commerce Act, a contract or signature can’t be denied enforceability just because it’s in electronic form.2Office of the Law Revision Counsel. 15 USC 7001 – General Rule of Validity Clicking “I agree,” typing your name in a signature field, or using a digital signing platform all count.
Integration Clauses
Many written contracts include an integration clause (sometimes called a merger clause) stating that the document is the entire agreement and no outside promises or side deals exist. Under the parol evidence rule, if you signed a contract with one of these clauses and the other party later claims you made a verbal side deal, that claim is almost certainly going nowhere. The practical takeaway: if a term matters to you, make sure it’s in the written document before you sign.
Implied Agreements
Not every agreement requires words. Implied agreements form through behavior and circumstances, and they come in two varieties.
An implied-in-fact agreement exists when the conduct of both parties shows they intended to make a deal, even though nobody said so out loud. Sitting down at a restaurant and ordering food is the classic example. You never explicitly promise to pay, but your behavior makes the obligation obvious. The same logic applies when you hand your keys to a valet or drop off clothes at a dry cleaner. Courts ask whether a reasonable person in that situation would expect to pay for the service received.
An implied-in-law agreement, or quasi-contract, isn’t really an agreement at all. It’s a legal fiction courts impose to prevent one party from unfairly benefiting at the other’s expense. If an unconscious accident victim receives emergency medical care, the patient never agreed to pay, but a court can create a quasi-contractual obligation to compensate the provider. The focus isn’t on what the parties intended; it’s on whether letting one side keep a benefit without paying would be unjust. When courts impose this kind of obligation, they usually measure damages using a standard called quantum meruit (Latin for “as much as one has deserved”), based on the market value of the services provided.
Bilateral and Unilateral Agreements
Agreements also differ in how they create obligations, and this distinction trips people up more than you’d expect.
A bilateral agreement is the most common structure. Both sides exchange promises: one party promises to deliver a product, the other promises to pay. Each person is both making and receiving a promise, and the deal is binding as soon as the promises are exchanged. An employment contract works this way. The employer promises to pay wages, and the employee promises to perform work. Neither side has to finish first for the agreement to be enforceable.
A unilateral agreement binds only one side, and only after the other side performs a specific act. The textbook example is a reward poster: an owner promises $500 to whoever finds and returns a lost dog. Nobody is obligated to search, but if someone finds the dog and brings it back, the owner must pay. The contract doesn’t exist until the performance is complete.3Legal Information Institute. Unilateral Contract If the offeror tries to revoke after someone has already started performing, most courts will protect the person who began the work.
Executory and Executed Agreements
These terms describe the status of an agreement rather than how it was formed. An executory agreement is one where obligations remain to be performed. If you sign a lease in January for an apartment you’ll move into in March, the lease is executory during that gap because neither side has fully performed. An executed agreement is one where all parties have completed their obligations. Once you’ve lived out the lease term and paid all rent, the agreement is fully executed. The distinction matters in bankruptcy, real estate closings, and other contexts where courts need to know whether a contract still carries unfulfilled duties.
Void and Voidable Agreements
Not every agreement that looks valid actually holds up. The law sorts problem agreements into two bins.
A void agreement has no legal effect from the start. It’s treated as though it never existed. Contracts with an illegal purpose fall here, as do agreements where a critical element like consideration was never present. Neither party can enforce a void agreement, and a court won’t step in to save it.
A voidable agreement is valid until the disadvantaged party decides to cancel it. Contracts signed by minors are the most common example. The minor can honor the deal or walk away from it (a right called disaffirmance), but the adult on the other side stays bound unless the minor cancels. Agreements signed under duress, fraud, or by someone who lacked mental capacity at the time follow the same pattern. The agreement stands unless the affected party acts to undo it.
Adhesion Contracts
An adhesion contract is a standardized, take-it-or-leave-it agreement drafted entirely by one side. Cell phone plans, software license agreements, and gym memberships are common examples. You can sign or walk away, but you can’t negotiate the terms. Courts generally enforce these, but they’ll strike down specific provisions that are unconscionable. Factors that make a clause unconscionable include extreme imbalance in bargaining power, confusing language a non-lawyer wouldn’t understand, and terms wildly inconsistent with what a reasonable person would expect.
Common Business and Employment Agreements
Businesses layer specialized agreements on top of the basic types above. Each one targets a specific risk.
Non-Disclosure Agreements
A non-disclosure agreement (NDA) prohibits one or both parties from sharing confidential information, such as trade secrets, client lists, or proprietary processes. NDAs are standard in technology, manufacturing, and any industry where competitive advantage depends on keeping information private. They typically define what counts as confidential, how long the obligation lasts, and what happens if someone breaches the terms. Most NDAs either work in both directions (mutual NDAs) or protect only the disclosing party (one-way NDAs).
Non-Compete Agreements
A non-compete agreement restricts an employee from working for a competitor or starting a competing business for a defined period within a specific geographic area after leaving their job. For these to be enforceable, most states require that the restrictions be reasonable in time, scope, and geography.
The rules for non-competes have been shifting. In 2024, the Federal Trade Commission issued a final rule that would have banned most new non-compete agreements nationwide, defining them as an unfair method of competition.4Federal Trade Commission. Noncompete Rule A federal court in Texas set the rule aside before it took effect, issuing a nationwide order blocking enforcement.5Congressional Research Service. Federal Courts Split on Legality of the FTCs NonCompete Rule As of early 2026, the FTC rule is not in effect, and non-compete enforceability continues to depend on state law. A handful of states ban them outright for most workers, while others enforce them as long as the restrictions are reasonable.
Service Level Agreements
A service level agreement (SLA) sets measurable performance standards for a vendor or service provider. SLAs are common in IT, cloud computing, and outsourced services. They define metrics like system uptime (often 99.9% or higher), response times for support requests, and penalties or credits if the provider misses those targets. Without an SLA, a client’s only remedy for poor service is a general breach-of-contract claim, which is harder to prove and slower to resolve.
Force Majeure Clauses
A force majeure clause excuses one or both parties from performing when extraordinary events beyond anyone’s control make performance impossible or impractical. Common triggers include natural disasters, wars, government-imposed restrictions, pandemics, and major infrastructure failures. These clauses drew intense attention during COVID-19, when businesses across industries invoked them to justify delayed or canceled performance.
Force majeure protections aren’t automatic. The affected party typically has to notify the other side promptly, provide evidence of the disruption, take reasonable steps to minimize damage, and resume performance once the event passes. The clause also won’t excuse you if you were already behind on your obligations before the event occurred or if the clause doesn’t specifically list the type of event that happened. Courts interpret these provisions narrowly, so the exact language in your contract matters more than general expectations about fairness.
What Happens When an Agreement Is Broken
A breach occurs when one party fails to perform an obligation under the agreement. The remedy depends on the type of deal and the harm caused. The most common is compensatory damages, meant to put the non-breaching party in the financial position they would have been in if the contract had been performed. When money can’t fix the problem, a court may order specific performance, forcing the breaching party to actually complete the deal. This is most common in real estate because every property is considered unique. Courts rarely order specific performance for employment or personal services since they won’t force someone to work against their will. A third option is rescission, which cancels the contract and tries to put both parties back where they started, often paired with restitution to return any benefits already exchanged.
Agreements can also be changed or ended by the parties themselves. Under common law, modifying a contract usually requires new consideration from both sides, a principle known as the pre-existing duty doctrine.6Legal Information Institute. Pre-Existing Duty Doctrine The UCC relaxes this for sales of goods, where a good-faith modification is enforceable without new consideration. To end an agreement cleanly, follow any termination provisions in the contract precisely. Ignoring notice requirements is a common mistake that turns a legitimate exit into a breach.