Ex parte Crow Dog was a United States Supreme Court case that dealt with the issue of tribal sovereignty. The case arose when a member of the Sioux tribe, Crow Dog, killed another member of the tribe, Spotted Tail. The US government charged Crow Dog with murder, but the Sioux tribe argued that they had the right to try and punish Crow Dog according to their own laws. The Supreme Court ultimately ruled in favor of the Sioux tribe, holding that the tribe had the right to try and punish its own members according to its own laws. The Court reasoned that the US government had no authority to interfere in the internal affairs of the tribe, and that the tribe had the right to self-governance. The ruling established the principle of tribal sovereignty, which has been used to protect the rights of Native American tribes ever since.

In Ex Parte Crow Dog, the Supreme Court was asked to determine whether a tribal court had jurisdiction over an Indian accused of murdering another Indian on a reservation. Justice Field delivered the dissenting opinion, arguing that Congress has exclusive power to regulate commerce with Native American tribes and their members. He argued that this power should extend to criminal matters as well since it is necessary for Congress to be able to protect its citizens from crime in order for trade and other activities between Indians and non-Indians on reservations or elsewhere in the United States. Furthermore, he argued that allowing tribal courts jurisdiction over such matters would lead to chaos because different tribes have different laws regarding crimes committed by one tribe member against another. Therefore, he concluded that only federal courts should have authority when it comes to prosecuting offenses committed by Indians against other Indians within Indian country or outside of it.