How was the Supreme Court founded?

The Supreme Court of the United States was established in principal by the United States Constitution. Within Article III of the Constitution, the judicial power of the United States is to be vested in "one supreme Court." It provides for Congress to create the lower courts as it sees fit. The Constitution also mentions that the Supreme Court will have jurisdiction over cases involving the states but allowed for Congress to establish its composition and responsibilities.

The Judiciary Act of 1789 established the Supreme Court with a chief justice and five associate justices. The number of justices in the court fluctuated throughout the 19th Century but a law in 1869 set the number at nine and it has remained that way ever since.