• The trial, in a courthouse in Norristown, Pa., near Philadelphia, will begin with opening statements by both sides.
• The once popular comedian and actor is charged with drugging and sexually assaulting a Temple University employee at his nearby home in 2004.
• Jurors were drawn from the Pittsburgh area, several hours away, because of concerns over pretrial publicity.
• The trial, expected to last two weeks, is the only criminal case to arise from the many accusations made against Mr. Cosby by women.
• Mr. Cosby has said he will not testify, but the complainant, Andrea Constand, is set to offer her account in what is expected to be the most dramatic moment in the trial.
The trial marks the end of a journey, and follows months of courtroom struggles by Mr. Cosby to have the charges — three counts of aggravated indecent assault filed in December 2015 — thrown out.
Mr. Cosby met Ms. Constand in November 2002 when he attended a basketball game at Temple University, his alma mater, in Philadelphia. Ms. Constand, who had been a high school basketball star in Canada, was the director of operations for the Temple women’s team.
Ms. Constand has described taking three pills at Mr. Cosby’s home and becoming completely immobilized, during which time, she has said, she was sexually molested.
Aggravated indecent assault carries a maximum sentence of 10 years.
Ms. Constand will likely face harsh questioning from the defense about why she kept in touch with Mr. Cosby after the alleged assault and why she took a year to take her complaint to the police.
Mr. Cosby, 79, who has said he will not testify, denies drugging her. He admits sexual contact but says it was part of a consensual romantic relationship.
The Cosby defense is led by Brian McMonagle, a prominent Philadelphia defense lawyer with a reputation for aggressive litigation, and Angela C. Agrusa of the Los Angeles law firm Liner.
Kevin R. Steele is the Montgomery County district attorney who helped reopen the investigation and bring the new charges against Mr. Cosby.
Camille Cosby, Mr. Cosby’s wife of 53 years, has not attended the pretrial hearings. It’s not clear whether she will be at the trial to support him.
Also present for many observers, of course, will be the memory of the man Mr. Cosby once was — the man behind Fat Albert and Dr. Cliff Huxtable on “The Cosby Show,” who also became something of a scold later in his life with his criticism of single motherhood and low-slung pants.
The dozens of other women who have come forward in recent years to say Mr. Cosby also assaulted them will not be testifying at the trial, though several may attend.
Ms. Constand’s complaint is the only one that has attracted criminal charges. For the many others, the statutes of limitations had run out — although the women may see a conviction as a vindication for themselves.
Judge Steven T. O’Neill, though, has allowed prosecutors to introduce one of the other many accusers to give her story in order to demonstrate a pattern in Mr. Cosby’s behavior. The woman, identified only as “Kacey,” says she was drugged and assaulted by Mr. Cosby in 1996.