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 Illinois, tortious interference with a contract occurs when a third party, who is not part of an existing contract, intentionally and improperly interferes with the contract, causing one of the parties to breach it and resulting in damages to the other party. To establish a claim for tortious interference in Illinois, the plaintiff must prove the existence of a valid and enforceable contract between the plaintiff and another party, the defendant's knowledge of this contract, intentional and unjustified inducement to breach the contract by the defendant, a subsequent breach of the contract caused by the defendant's wrongful conduct, and damages resulting from the breach. Illinois also recognizes claims for tortious interference with a prospective economic advantage, which protects business relationships that have not yet been formalized into a contract. However, not all interferences are actionable; actions that are considered legitimate competition or are done with justification may not constitute tortious interference.