Original jurisdiction refers to a courts authority to hear and decide a case for the first time before any appellate review occurs. In common law legal systems, original jurisdiction of a court is the power to hear a case for the first time, as opposed to appellate jurisdiction, when a higher court has the power to review a lower courts decision.

In the United States, the Supreme Court has both original and appellate jurisdiction. Original jurisdiction means that the Supreme Court is the first and only court to hear a case, and it is limited to disputes between states or disputes arising among ambassadors and other high-ranking ministers. Congress codified the original jurisdiction of the Supreme Court by statute in 28 U.S.C. § 1251. Section 1251(a) provides that the Supreme Court has not only original jurisdiction but also exclusive jurisdiction over controversies between two or more States. Section 1251(b) provides that the Supreme Court has original, but not exclusive, jurisdiction over certain cases.

Most of the cases that the United States Supreme Court hears are on appeal from lower courts, either federal district courts, federal courts of appeal, or state courts. However, in a limited class of cases, the Court has original jurisdiction to consider the facts and the law of a case without it having first been passed on by a lower court. Currently, the only original jurisdiction cases commonly handled by the Supreme Court of the United States are disputes between two or more U.S. states, typically regarding boundary lines, water claims, or other property issues.

In India, the Supreme Court has original, appellate, and advisory jurisdiction. Its exclusive original jurisdiction extends to all cases between the Government of India and the States of India or between Government of India and states on one side and one or more states on the other side or cases between different states.

In summary, original jurisdiction refers to a courts power to hear a case for the first time, as opposed to appellate jurisdiction, which is the power to review a lower courts decision. The Supreme Court of the United States has original jurisdiction over select cases, namely those affecting Ambassadors, other public Ministers and Consuls, and those in which one of the 50 states is a party.