The Pennsylvania AO-441 Summons on Third-Party Complaint is a document used by a court when a plaintiff is suing two or more defendants. It is also known as a third-party summons. The summons informs the third-party defendant that they are being sued, and gives them specific instructions on how to respond to the complaint. There are three types of Pennsylvania AO-441 Summons on Third-Party Complaint: 1. The AO-441A Summons on Third-Party Complaint, which is used when the plaintiff is suing multiple defendants in a single action. 2. The AO-441B Summons on Third-Party Complaint, which is used when the plaintiff is suing multiple defendants in separate actions. 3. The AO-441C Summons on Third-Party Complaint, which is used when the plaintiff is suing one defendant in multiple actions. The AO-441 Summons on Third-Party Complaint is a document that informs the third-party defendant that they are being sued and outlines the specific instructions for responding to the complaint. It must be served on the third-party defendant in order for the case to move forward.