The story that has dominated US politics for weeks is now centre stage in a Senate committee room.
Brett Kavanaugh, the man nominated for a vacant post on the Supreme Court, and a woman accusing him of sexual assault are both testifying.
Mr Kavanaugh has denied allegations by Christine Blasey Ford, along with those of a number of other women.
The nine-member Supreme Court plays a vital role in US political life, as it has the final say on US law.
This includes highly contentious social issues, such as abortion, and challenges to government policy.
President Donald Trump has called the hearing an "important day in the history of our country".
Doug_Demuro2018-09-27 22:46:52
What did Christine Blasey Ford say ?
No-one had heard from 51-year-old Professor Ford publicly previously since the allegations arose.
After addresses by the leading Republican and Democrat members, Prof Ford delivered her opening statement, at times appearing close to tears.
In her prepared testimony, Prof Ford said : "I am here today not because I want to be. I am terrified. I am here because I believe it is my civic duty to tell you what happened to me while Brett Kavanaugh and I were in high school."
She alleged Mr Kavanaugh and his friend Mark Judge locked her in a bedroom during a small gathering at a house in a Washington DC suburb in the summer of 1982.
#WhyIDidntReport supports Professor Ford
She said Mr Kavanaugh tried to remove her clothing, pinned her to a bed and groped her, when she was 15 and he was 17. Both men were "drunkenly laughing", she said.
She added: "Brett's assault on me drastically altered my life. For a very long time, I was too afraid and ashamed to tell anyone the details."
The 21 senators on the committee will have five minutes each to ask her questions.
The 10 Democrats will pose questions themselves and are expected to ask how the incident affected her and why it took her so long to talk about it.
The 11 Republicans, all men, are expected to defer most of their questions to a female lawyer, Phoenix prosecutor Rachel Mitchell.
Prof Ford will reportedly then leave the room and Mr Kavanaugh will enter. Prof Ford had earlier asked not to be in the same room as the judge.
Mr Kavanaugh, 53, will deliver his statement and the same round of questioning will follow.
A Democratic Party aide told Associated Press that its senators would try to make him look nervous and would address inconsistencies in his earlier statements.