<P> Since 1789, Congress has occasionally altered the size of the Supreme Court, historically in response to the country's own expansion in size . An 1801 act would have decreased the Court's size to five members upon its next vacancy . However, an 1802 act negated the effects of the 1801 act upon the Court before any such vacancy occurred, maintaining the Court's size at six members . Later legislation increased its size to seven members in 1807, to nine in 1837, and to ten in 1863 . An 1866 act was to have reduced the Court's size from ten members to seven upon its next three vacancies, and two vacancies did occur during this period . However, before a third vacancy occurred, the Judiciary Act of 1869 intervened, restoring the Court's size to nine members, where it has remained since . </P> <P> While the justices of the Supreme Court are appointed for life, many have retired or resigned . Beginning in the early 20th century, many justices who left the Court voluntarily did so by retiring from the Court without leaving the federal judiciary altogether . A retired justice, according to the United States Code, is no longer a member of the Supreme Court, but remains eligible to serve by designation as a judge of a U.S. Court of Appeals or District Court, and many retired justices have served in these capacities . Historically, the average length of service on the Court has been less than 15 years . However, since 1970 the average length of service has increased to about 26 years . </P> <P> There are currently nine justices serving on the Supreme Court; listed in order of seniority, they are: </P> <Ul> <Li> John Roberts, Chief Justice since September 29, 2005 Age 7004231320000000000 ♠ 63 </Li> </Ul>

How many justices currently serve on the us supreme court