The trial of US comedian and actor Bill Cosby for sexual assault has begun in Pennsylvania.
Former university employee Andrea Constand alleges he drugged and molested her in 2004.
Mr. Cosby, 79, says he is innocent and the encounter was consensual. The trial is expected to last about two weeks.
It is being seen as the biggest US celebrity court case since the murder trial of former American football player OJ Simpson in 1995.
Several of Mr. Cosby’s co-stars from the 1984-1992 sitcom The Cosby Show are expected to attend the trial in Norristown, outside Philadelphia. One of them, Keshia Knight Pulliam, accompanied him into court.
More than 100 journalists are expected to cover the trial.
Mr. Cosby faces three counts of aggravated indecent assault. Each count carries a maximum sentence of 10 years and a fine of up to $25,000 (£19,500).
In 2004 Ms Constand was 31 when she visited Mr. Cosby’s home seeking career advice after befriending him through Temple University in Philadelphia, where he served on the board of trustees.
She said Mr. Cosby gave her three blue pills which made her legs feel “like jelly” and that he then began to touch her inappropriately.
In 2006, the comedian settled with Ms Constand after providing an undisclosed cash sum to her.
At least 50 women have accused Mr. Cosby of sexual assault, but he only faces charges in Ms Constand’s case because of statutes of limitations.
Mr. Cosby says his encounter with Ms Constand was consensual.
He also says he offered women drugs as a way to encourage them to relax rather than a way to render them helpless.
Why is Bill Cosby important?
Mr. Cosby is best known for his role as the father in the television hit The Cosby Show, which was a huge hit in the US and around the globe.
At one point he was the highest-paid actor in the US.
He was born in Philadelphia and started his career as a stand-up comedian in 1962, debuting on NBC’s The Tonight Show in 1963.
In 1965, he became the first black actor to star in a drama series in the US, in the espionage show I Spy. He earned three consecutive best actor Emmys for his role, at a time of high race tensions in the US.
In 2013 he did a national stand-up tour and received rave reviews. After that, several women began to come forward with allegations of sexual assault, some going back nearly 30 years.