The responsibility for appointing Supreme Court justices in the United States lies with the President. Upon a vacancy in the Supreme Court, the President nominates a candidate, usually after consultation with legal experts and political advisors, ensuring the pick aligns with their judicial philosophy. The nominee must then be confirmed by the Senate, which holds hearings and votes on the appointment. This process reflects the checks and balances inherent in the U.S. government, where the executive and legislative branches collaborate in shaping the judicial branch's composition.