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 Delaware, tortious interference with contract is recognized as a legal cause of action. This occurs when a third party, who is not part of an existing contract, intentionally interferes with the contractual relationship, causing one of the parties to breach the contract and resulting in damages to the other party. To establish a claim for tortious interference in Delaware, the plaintiff must prove the existence of a valid contract, knowledge of the contract by the interferer, an intentional act that caused the breach or termination of the contractual relationship, and resultant damages. Delaware law also recognizes claims for interference with prospective contractual relations, where there is no existing contract but a business expectancy that is knowingly and improperly interfered with by a third party. However, not all interferences are actionable; some are considered legitimate competitive behavior. The distinction often hinges on the presence of improper motives or methods. An attorney can help determine whether a specific instance of interference may constitute a legal claim under Delaware law.