In Ex Parte: In the Matter of William Wells, the Supreme Court was asked to determine whether a slave who had been taken from his owner in Missouri and brought into Illinois could be held as property. The court ruled that since slavery was prohibited by state law in Illinois, Wells could not be held as property. Furthermore, it found that even if he were still considered a slave under Missouri law, he would still have rights under the Constitution's Privileges and Immunities Clause which protected him from being deprived of liberty without due process of law. This ruling established an important precedent for future cases involving slaves who traveled across state lines or territories where slavery was illegal.

In Ex Parte: In the Matter of William Wells, the Supreme Court was asked to decide whether a slave owner had the right to take his slaves into free states and territories. The majority opinion held that Congress did not have authority over slavery in these areas, so it could not be prohibited by federal law. However, Justice Curtis dissented from this decision. He argued that Congress had clear constitutional power to regulate slavery in all places under its jurisdiction and thus should be able to prohibit it in any state or territory where it is found. Furthermore, he argued that even if Congress lacked such power directly, they still had indirect means of regulating slavery through their control over interstate commerce and foreign relations with other countries who may recognize fugitive slaves as citizens upon entering their borders. Ultimately, Justice Curtis concluded that while there may be some practical difficulties associated with enforcing such laws across multiple jurisdictions without infringing on state sovereignty rights; nevertheless those issues were outweighed by the moral imperative for freedom which must prevail throughout our nation's boundaries regardless of individual state laws on the matter at hand.