http://en.wikipedia.org/wiki/Chief_Justice_of_the_United_States
The Chief Justice is nominated by the President of the United States and confirmed to sit on the Court by the United States Senate. The U.S. Constitution states that all justices of the court "shall hold their offices during good behavior," meaning that the appointments only end when a justice dies in office, resigns, or is impeached by the United States House of Representatives and convicted at trial by the Senate. The salary of the Chief Justice is set by Congress; the Constitution prohibits Congress from lowering the salary of any judge, including the Chief Justice's, while that judge holds his or her office. As of 2010, the salary is $223,500 per year, which is slightly higher than that of the Associate Justices.[2]
While the Chief Justice is appointed by the President, there is no specific constitutional prohibition against using another method to select the Chief Justice from among those Justices properly appointed and confirmed to the Supreme Court, and at least one scholar has proposed that presidential appointment should be done away with, and replaced by a process that permits the Justices to select their own Chief Justice.[3]
Three serving Associate Justices have received promotions to Chief Justice; Edward Douglass White in 1910, Harlan Fiske Stone in 1941, and William Rehnquist in 1986. Associate Justice Abe Fortas was nominated to position of Chief Justice of the United States, but his nomination was filibustered by Senate Republicans in 1968. Despite the failed nomination, Fortas remained an Associate Justice until his resignation two years later. Most Chief Justices, including John Roberts, have been nominated to the highest position on the Court without any previous experience on the Supreme Court; indeed some, such as Earl Warren, received confirmation despite having no prior judicial experience.
There have been 21 individuals nominated for Chief Justice, of whom 17 have been confirmed by the Senate, although a different 17 have served. The second Chief Justice, John Rutledge, served in 1795 on a recess appointment, but did not receive Senate confirmation. Associate Justice William Cushing received nomination and confirmation as Chief Justice in January 1796, but declined the office; President Washington then nominated, and the Senate confirmed, Oliver Ellsworth, who served instead. The Senate subsequently confirmed President Adams's nomination of John Jay to replace Ellsworth, but Jay declined to resume his former office, citing the burden of riding circuit and its impact on his health, and his perception of the Court's lack of prestige. Adams then nominated John Marshall, whom the Senate confirmed shortly afterward.[citation needed]
When the Chief Justice dies in office or is otherwise unwilling or unable to serve, the duties of the Chief Justice temporarily are performed by the most senior sitting associate justice, who acts as Chief Justice until a new Chief Justice is confirmed.