In contract law, a mistake is an erroneous belief, at contracting, that certain facts are true. It can be argued as a defense, and if raised successfully can lead to the agreement in question being found void ab initio or voidable, or alternatively an equitable remedy may be provided by the courts. Common law has identified three different types of mistake in contract: the 'unilateral mistake', the 'mutual mistake' and the 'common mistake'. The distinction between the 'common mistake' and the 'mutual mistake' is important.
Another breakdown in contract law divides mistakes into four traditional categories: unilateral mistake, mutual mistake, mistranscription, and misunderstanding.The law of mistake in any given contract is governed by the law governing the contract. The law from country to country can differ significantly. For instance, contracts entered into under a relevant mistake have not been voidable in English law since Great Peace Shipping v Tsavliris (International) Ltd (2002).