"The role of the Senate in the confirmation process is defined in the Constitution. Article II, Section 2 provides that the President 'shall nominate, and by and with the Advice and Consent of the Senate, shall appoint high government officials.' All positions requiring confirmation are set by statute. Senate Rule XXXI regulates proceedings on nominations in executive sessions ('executive' in this case refers to executive business, not to a closed or secret session). Each Senate committee may adopt its own procedures as long as they do not conflict with Senate rules. For more information on legislative process, see [http://www.crs.gov/products/guides/guidehome.shtml]. The Senate gives its advice and consent to presidential appointments to the Supreme Court and to high-level positions in the Cabinet departments and independent agencies. The Senate also confirms appointments of members of regulatory commissions, ambassadors, federal judges, U.S. attorneys, and U.S. marshals. There are over 2,000 of these appointments. Appointees named to be Cabinet secretaries and Supreme Court justices receive the Senate's closest scrutiny due to the significance of these positions. About 99% of all presidential appointments are approved."
CRS Report for Congress, RS20986