Contracts set out the rights and obligations of the parties to a transaction. One useful way to classify them is by who makes a promise. In a unilateral contract, only one party promises, and the promise becomes binding when the other party performs a specific act. In a bilateral contract, both parties promise something to each other.
Knowing which one you are dealing with matters for compliance, for securing your rights and for avoiding disputes. This guide explains both types with examples, sets out the key differences and covers how to manage the obligations each creates. It is general information, not legal advice, and the rules vary by jurisdiction.
What is a unilateral contract?
A unilateral contract is a one sided agreement. One party, the promisor, commits to do something if another party performs a specified act. The other party is not obliged to act at all. If they do, the promisor must keep the promise.
Examples
- Bug bounty programs: a software company promises a reward to anyone who reports a qualifying security flaw. The obligation arises only when a valid report is submitted
- Referral programs: a business offers a discount or credit to customers who bring in a new buyer
- Money back guarantees: a company promises a refund if a customer is dissatisfied and makes a claim within the stated terms
- Rewards and contests: a published reward for returning lost property, or a prize for completing a challenge
- Sales bonuses: a bonus promised for hitting a defined target
Insurance policies are sometimes described as unilateral in character, because the insurer's duty to pay depends on an insured event, but in most cases premiums and coverage create commitments on both sides. Classification can depend on how the agreement is written and the law that applies.
Key characteristics
- One obligation: only the promisor is bound, and only once the act is completed
- Acceptance by performance: the other party accepts by doing the act, not by signing
- Clear terms: the act required and the reward offered must be stated precisely
Businesses use unilateral contracts to encourage actions without asking for an upfront commitment. They are flexible for the acceptor, focus effort on a defined goal and cost the promisor nothing unless the condition is met.
What is a bilateral contract?
A bilateral contract is an exchange of promises. Each party commits to do something for the other, and both are bound from the moment the contract is formed, before either has performed.
Examples
- Supplier agreements: the supplier promises to deliver goods or services, and the buyer promises to pay
- Software subscriptions: the provider promises access and support, and the customer promises to pay fees and follow usage terms
- Employment contracts: the employee promises to work, and the employer promises to pay salary and benefits
- Leases: the landlord promises use of the property, and the tenant promises rent and care of it
- Master service agreements: both parties commit to a framework of terms for future work
Key characteristics
- Mutual obligations: both parties owe performance
- Binding on formation: the promises are enforceable once the contract is agreed
- Negotiated terms: price, scope, service levels, liability and termination are usually negotiated
Most of the agreements an enterprise manages are bilateral. See master service agreement.
What are the key differences?
| Aspect | Unilateral contract | Bilateral contract |
|---|---|---|
| Who promises | One party | Both parties |
| How it is accepted | By performing the act | By agreeing to the terms |
| When obligations start | When the act is completed | When the contract is formed |
| Can the other party walk away? | Yes, they never had to act | No, both are bound |
| Typical uses | Rewards, guarantees, incentives | Supply, services, software, employment, leases |
| Main risk | Unclear conditions lead to disputes about whether the act was done | Missed obligations and breach on either side |
Why does the distinction matter?
Compliance and rights
In a bilateral contract you owe performance from day one, so you need to know your obligations as well as the other side's. In a unilateral contract your obligation is conditional, so the condition must be clear enough that you can tell when it has been met.
Avoiding disputes
Disputes in unilateral contracts usually turn on whether the act was performed as required: was the bug in scope, was the refund claimed in time? Disputes in bilateral contracts usually concern whether a promise was kept: was delivery on time, did the service meet the agreed level? Precise drafting prevents both. See breach of contract.
Revocation
Questions about when a promisor can withdraw a unilateral offer, especially once the other party has started performing, depend on the governing law. Legal teams should set out revocation terms clearly in programs such as rewards or bounties.
How should teams manage both types?
Whatever the type, the work is the same: store the agreement where it can be found, record the obligations and conditions, assign owners and track performance. A contract repository that classifies agreements by type, and extracts who owes what, makes that practical across thousands of contracts.
In Contractflow, Aavenir AI reads each agreement and extracts obligations for both parties, and Obligationflow assigns them to owners with reminders. A person approves every extracted result.
The bottom line
A unilateral contract binds one party when the other performs an act. A bilateral contract binds both parties from the start. Most enterprise agreements are bilateral, but both types need clear terms and tracked obligations to avoid disputes.