Slacum v. Pomeroy was a case heard by the United States Supreme Court in 1810. The dispute arose when William Slacum, an officer of the US Navy, sued John Pomeroy for damages to his ship during a voyage from Philadelphia to New York City. Slacum argued that he had been promised safe passage and that Pomeroy had failed to provide it due to negligence on his part. The court found in favor of Slacum and awarded him $1,000 in damages plus costs associated with bringing suit against Pomeroy. This decision established important precedent regarding contracts between private individuals and government officials as well as providing guidance on how courts should interpret such agreements going forward.

In Slacum v. Pomeroy, the Supreme Court was asked to decide whether a state court had jurisdiction over a case involving two citizens of different states. The majority opinion held that it did not have such jurisdiction and dismissed the appeal. However, Justice Story dissented from this decision on the grounds that there is no constitutional provision which explicitly denies state courts jurisdiction in cases between citizens of different states. He argued that if Congress has not acted to limit or deny such power then it should be assumed that they intended for state courts to retain their traditional authority in these matters unless specifically prohibited by law or Constitution. Furthermore, he noted that allowing each State's judiciary system to adjudicate disputes between its own citizens and those of other States would promote uniformity among laws throughout the Union as well as provide an efficient means for resolving conflicts without resorting to federal intervention every time one arises.