Ex parte Pennsylvania is a United States Supreme Court case that dealt with the issue of whether a state can be sued in federal court by another state. The case arose when Pennsylvania sued Maryland in federal court for failing to pay a debt that was due to Pennsylvania. Maryland argued that it could not be sued in federal court because it was a sovereign state. The Supreme Court held that a state can be sued in federal court by another state. The Court reasoned that the Constitution grants the federal government the power to hear cases between states, and that the federal government has the power to hear cases between states. The Court also noted that the Constitution does not grant states immunity from suit in federal court. The Court also held that the Eleventh Amendment does not bar a state from being sued in federal court by another state. The Court reasoned that the Eleventh Amendment only bars suits against a state by citizens of another state, and not suits between states. The Court's decision in Ex parte Pennsylvania established that states can be sued in federal court by other states. This decision has been cited in numerous cases since then, and has been an important precedent in the development of federal court jurisdiction.

In Ex Parte Pennsylvania, the Supreme Court was asked to decide whether a state could be sued in federal court without its consent. The majority opinion held that states were not subject to suit in federal court without their consent. However, Justice Field dissented from this decision and argued that the Constitution did not grant any special immunity from suit for states. He reasoned that since citizens of one state can sue citizens of another state in federal courts, then it logically follows that a citizen should also have the right to sue his or her own state government when necessary. Furthermore, he noted that if Congress had intended for states to enjoy such an immunity they would have explicitly stated so within the text of the Constitution itself; however no such language exists within its pages. Thus Justice Field concluded by arguing against granting any special privileges or immunities for states which are not enjoyed by individuals under similar circumstances and urged his colleagues on the bench to reconsider their ruling on this matter as soon as possible