Currently, the number of justices on the Supreme Court of the United States is nine, but it has varied through history. Justices are nominated by the president and must be approved by the Senate; once appointed, they have life tenure, which means that they may serve until they decide to retire. The Constitution gives Congress the power to set the number of justices who serve, and that number has changed several times since the court's inception. The first U.S. Supreme Court in 1790 had six justices. The number has been as low as five and as high as ten, but it has remained at nine since 1869.
In the U.S., the Supreme Court is the highest tier of the federal judiciary system. As such, the decisions of the justices are binding because there is no higher court to which to appeal. The Supreme Court has the power to decide if laws are allowable under the Constitution, and this authority allows it to exert considerable influence on matters of public policy. Justices are chosen by the president, but those nominations must be approved by the Senate. According to the Constitution, appointment to the U.S. Supreme Court is valid for a lifetime "during good behavior," and justices may serve until they die or choose to retire.
Article III of the U.S. Constitution gives Congress the power to set the number of justices on the Supreme Court. It currently stands at nine, with one chief justice and eight associate justices. Since the Supreme Court was introduced in 1790 with six justices, there have been several variations to the number. When a justice died in 1801, Congress lowered the number to five to prevent President Thomas Jefferson, who they disagreed with on many issues, from making an appointment. When the next Congress took office, the number was returned to six, where it remained for several years.
The next change came in 1807, when Congress raised the number to seven, with another increase to nine in 1837. The amount remained nine for quite a while, but in 1863 during the Civil War, it was raised to ten. After the war ended, there was a lot of friction between Congress and President Andrew Johnson; as a result, Congress passed a law that the next three justices to leave the Court would not be replaced, potentially lowering the number of justices to seven again. The last successful change was in 1869, when Congress passed the Judiciary Act, which increased it back to nine. In 1937, President Franklin D. Roosevelt attempted to "pack the court" by raising the number of justices to 15; this attempt, however, was unsuccessful.