The Chief Justice of the United States is the head of the United States federal court system (the judicial branch of the federal government of the United States) and the chief judge of the Supreme Court of the United States. The Chief Justice is one of nine Supreme Court justices; the other eight are the Associate Justices of the Supreme Court of the United States. From 1789 until 1866, the office was known as the Chief Justice of the Supreme Court.
The Chief Justice is the highest judicial officer in the country, and acts as a chief administrative officer for the federal courts and appoints the director of the Administrative Office of the United States Courts. The Chief Justice also serves as a spokesperson for the judicial branch.
The Chief Justice leads the business of the Supreme Court. He presides over oral arguments before the Court. When the Court renders an opinion, the Chief Justice—when in the majority—decides who writes the Court's opinion. Finally, the Chief Justice has significant agenda-setting power over the Court's meetings. In the case of an impeachment of a President of the United States, which has occurred twice, the Chief Justice presides over the trial in the Senate. In modern tradition, the Chief Justice also has the ceremonial duty of administering the oath of office of the President of the United States.
The first Chief Justice was John Jay. The 17th and current Chief Justice is John G. Roberts, Jr.