This Practice Note considers the legal concept of mistake in contract law. It examines common mistake, mutual mistake, unilateral mistake, mistake as to identity and mistake as to the document signed (non est factum). It also considers the impact of each of these types of mistake on the contract and the correction of mistakes by rectification or construction.

For guidance on dealing with mistakes in the execution of documents, see Practice Note: Deeds鈥擣ailure to comply with formalities and other defects and our Execution collection, in particular, The Basics鈥擰&As鈥擬istakes in executing documents.

For more guidance where parties choose to correct a mistake by agreeing an amendment to the operative parts of a contract, see Practice Note: Contract variation.