Unconscionability (sometimes known as unconscionable dealing/conduct in Australia) is a doctrine in contract law that describes terms that are so extremely unjust, or overwhelmingly one-sided in favor of the party who has the superior bargaining power, that they are contrary to good conscience. Typically, an unconscionable contract is held to be unenforceable because no reasonable or informed person would otherwise agree to it. The perpetrator of the conduct is not allowed to benefit, because the consideration offered is lacking, or is so obviously inadequate, that to enforce the contract would be unfair to the party seeking to escape the contract.

Unconscionability is determined by examining the circumstances of the parties when the contract was made, such as their bargaining power, age, and mental capacity. Other issues might include lack of choice, superior knowledge, and other obligations or circumstances surrounding the bargaining process. Unconscionable conduct is also found in acts of fraud and deceit, where the deliberate misrepresentation of fact deprives someone of a valuable possession. When a party takes unconscionable advantage of another, the action may be treated as criminal fraud or the civil action of deceit.

For the defense of unconscionability to apply, the contract has to have been unconscionable at the time it was made; later circumstances that make the contract extremely one-sided are irrelevant. There are generally no standardized criteria for determining unconscionability; it is a subjective judgment by the judge, not a jury, and is applied only when it would be an affront to the integrity of the judicial system to enforce such a contract. Upon finding unconscionability a court has a great deal of flexibility on how it remedies the situation. It may refuse to enforce the contract against the party unfairly treated on the theory that they were misled, lacked information, or signed under duress or misunderstanding; it may refuse to enforce the offending clause, or take other measures it deems necessary to have a fair outcome. Damages are usually not awarded.