Tortious interference with contract—also known as intentional interference with contractual relations or business expectancy—is a civil claim or cause of action based on interference with a contract or a prospective contract that is about to be completed—by a person or entity who is not a party to the contract (third party).

A claim for tortious interference is based on the idea that the third party encouraged or induced one of the parties to the contract to breach the contract, causing damages to the nonbreaching party, who may sue the third party to recover those damages or losses. In some states there is a requirement that the interference be done maliciously or without justification.

Laws regarding claims for tortious interference with contract vary from state to state. Some states have broadened the protections against interference beyond situations where there is an existing contract and recognize claims for interference with prospective economic advantage or business relations.

But whether there is an existing contract or not, some instances of interference will not create legal liability and will be recognized as legitimate competitive activity, for example.

In California, tortious interference with contract, also known as intentional interference with contractual relations, is recognized as a legal claim. This occurs when a third party, who is not part of an existing contract, intentionally acts to cause one of the contracting parties to breach that contract, resulting in harm to the other party. The elements of this tort typically include the existence of a valid contract, the third party's knowledge of the contract, intentional acts to induce a breach or disruption of the contract, actual breach or disruption of the contractual relationship, and resulting damage to the nonbreaching party. California also recognizes a related claim for interference with prospective economic advantage, which protects business relationships even in the absence of a formal contract, provided that there was a reasonable probability of future economic benefit that was disrupted by the third party's intentional actions. However, not all interferences are actionable; California law allows for defenses such as competition, where interference is considered a legitimate business practice, provided it is done without employing wrongful means.