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 Pennsylvania, tortious interference with contract, also known as intentional interference with contractual relations, is recognized as a legal cause of action. This occurs when a third party, who is not part of an existing contract, intentionally causes one of the contracting parties to breach that contract, resulting in damages to the other party. The nonbreaching party can then sue the third party for those damages. Pennsylvania law requires the plaintiff to prove that the interference was intentional and resulted in a breach of contract, causing harm. Additionally, the interference must be without justification; Pennsylvania recognizes the concept of privilege or justification in certain circumstances, such as legitimate competition. The state also acknowledges claims for interference with prospective contractual relations, where there is no existing contract but a likely future contract that has been disrupted by the third party's actions. To succeed in a claim for tortious interference in Pennsylvania, the plaintiff must typically establish the existence of a contractual relationship or prospective business opportunity, intentional and unjustified interference by the third party, and resultant damage.