For the first time in history, three women now serve together on the U.S. Supreme Court. Elena Kagan has been sworn in as the high court's 112th justice.
Chief Justice John Roberts administered the oath of office to Elena Kagan Saturday at the Supreme Court.
Kagan joins justices Ruth Bader Ginsburg and Sonia Sotomayor as the largest number of women ever to serve together on the nine-member Supreme Court.
On Friday, President Barack Obama called that an "exhilarating development." "A sign of progress that I relish, not just as a father who wants limitless possibilities for my daughters, but as an American proud that our Supreme Court will be a little more inclusive, a little more representative, more reflective of us as a people than ever before," he said.
The Senate confirmed President Obama's nomination of Kagan on Thursday, by a vote of 63-to-37. Supreme Court justices are appointed for life.
The 50-year-old Kagan had been the U.S. Solicitor General, representing the federal government before the Supreme Court.
Most Senate Republicans voted against Kagan's confirmation, saying she has never been a judge and lacks judicial experience.
Kagan will take the place of 90-year-old Justice John Paul Stevens, who recently retired. Stevens was widely seen as the most liberal justice on the high court.
The new justice is not expected to change the court's ideological balance. Five of the nine justices are regarded as leaning conservative.
The Supreme Court session begins October 1.
Overall, Kagan is the fourth woman on the high court. Sandra Day O'Connor was the first. She was appointed by President Ronald Reagan in 1981, and retired in 2006..