Pennsylvania Join an Additional Defendant is a legal process used in civil cases when a defendant wants to join another party as a defendant in a case. This process is also known as imp leader. It allows the defendant to add a third party to the lawsuit who may be liable for all or part of the damages sought by the plaintiff. There are two types of Join an Additional Defendant: permissive and compulsory. Permissive joiner allows the defendant to voluntarily join a third party to the lawsuit, while compulsory joiner requires the court’s approval. Both processes are governed by Rules 1033 and 1034 of the Pennsylvania Rules of Civil Procedure.