Pennsylvania Petition For Joiner of Additional Defendant is a document used to add a defendant to an existing civil lawsuit in the state of Pennsylvania. The petition must be filed with the court in which the initial lawsuit was filed and must include the name of the additional defendant, the name of the plaintiff, and the name of the original defendant. It must also include the nature of the claim, the relief sought, and any prior court orders or judgments concerning the original action. There are two types of Pennsylvania Petition For Joiner of Additional Defendant: voluntary joiner and involuntary joiner. Voluntary joiner occurs when the plaintiff and the additional defendant agree to join the lawsuit. Involuntary joiner is when the additional defendant does not voluntarily agree to join the lawsuit, and the plaintiff must make a formal petition to the court to join the defendant.