On October 31, 2005, President George W. Bush nominated Samuel Alito for Associate Justice of the Supreme Court of the United States to replace retiring Justice Sandra Day O'Connor. Alito's nomination was confirmed by a 58–42 vote of the United States Senate on January 31, 2006.

Alito was a judge on the United States Court of Appeals for the Third Circuit at the time of his nomination to the Court. He had been appointed to that position by the president's father, President George H. W. Bush in 1990. Leonard Leo played a crucial role in successfully shepherding Alito's appointment through the Senate.

On October 31, 2005, President George W. Bush nominated Samuel Alito, a federal appeals court judge with a conservative record, to succeed retiring Justice Sandra Day O'Connor on the United States Supreme Court. The announcement came four days after the president's initial choice, Harriet Miers, withdrew herself from the confirmation process. Before Bush chose Miers, Alito's name was among those frequently mentioned a possible candidate for the seat.

In announcing Alito's nomination, Bush stated, "He's scholarly, fair-minded and principled and these qualities will serve him well on the highest court in the land. [His record] reveals a thoughtful judge who considers the legal merits carefully and applies the law in a principled fashion. He has a deep understanding of the proper role of judges in our society. He understands judges are to interpret the laws, not to impose their preferences or priorities on the people." Alito, in accepting the nomination, said, "Federal judges have the duty to interpret the Constitution and the laws faithfully and fairly, to protect the constitutional rights of all Americans, and to do these things with care and with restraint, always keeping in mind the limited role that the courts play in our constitutional system. And I pledge that if confirmed I will do everything within my power to fulfill that responsibility."

The American Civil Liberties Union formally opposed Alito's nomination. The ACLU has only taken this step three other times in its entire history, the last time having been with the rejected nomination of Robert Bork. In releasing their report on Alito, ACLU executive director Anthony Romero justified the decision by saying that "At a time when our president has claimed unprecedented authority to spy on Americans and jail terrorism suspects indefinitely, America needs a Supreme Court justice who will uphold our precious civil liberties. Unfortunately, Judge Alito's record shows a willingness to support government actions that abridge individual freedoms."

Democratic senator Barack Obama said, "Though I will reserve judgment on how I will vote on Judge Alito's nomination until after the hearings, I am concerned that President Bush has wasted an opportunity to appoint a consensus nominee in the mold of Sandra Day O'Connor and has instead made a selection to appease the far right-wing of the Republican Party." Another Democratic senator, John Kerry, stated: "Every American should be deeply concerned that the far right wing which prevented Harriet Miers from even receiving a Senate hearing is celebrating Judge Alito's nomination and urging the Senate to rubber-stamp the swing vote on our rights and liberties. Has the right wing now forced a weakened President to nominate a divisive justice in the mold of Antonin Scalia?"

Senator Lincoln Chafee stated on January 30, 2006, "I am a pro-choice, pro-environment, pro-Bill of Rights Republican, and I will be voting against this nomination."

NARAL Pro-Choice America announced its opposition to Alito's nomination by saying "In choosing Alito, President Bush gave in to the demands of his far-right base and is attempting to replace the moderate O'Connor with someone who would move the court in a direction that threatens fundamental freedoms, including a woman's right to choose as guaranteed by Roe v. Wade."