With the streets outside the courthouse lined with television trucks, Cosby arrived arm-in-arm with Keshia Knight Pulliam, who played his daughter Rudy Huxtable on "The Cosby Show." The courtroom was packed with members of the public and media.
Cosby faces three counts of aggravated indecent assault, and he has pleaded not guilty to the charges.
Cosby has said he does not plan to testify. His deposition from Constand's civil suit will stand as his explanation of what happened -- which means the trial likely will hinge on a classic case of "he said, she said."
In opening statements, Assistant District Attorney Kristen Feden told jurors that when Cosby "handed those pills to Andrea he knew what affect it would take" and he knew Constand would not be able to refuse his advances.
"Trust, betrayal, and the inability to consent. That's what this case is about. ... This is a case about a man, this man," she said, pointing to Cosby, "who used his power and his fame and his previously practiced method of placing a young trusting woman in an incapacitated state so that he could sexually pleasure himself so that she couldn't say no."
The district attorney at the time of the alleged assault declined to press charges, and in 2006 Cosby settled a civil suit with Constand that remained sealed for almost a decade.
'Like Andrea ...'
Defense attorney Brian McMonagle seized on the original prosecutor not leveling charges against Cosby, saying the case was "exhaustively investigated" at the time.
"Their investigation revealed that Andrea Constand had been untruthful time and time and time again," he said.
Though more than 50 women have accused the former "I Spy" star of assault, the trial will focus on the testimony of Constand and one other accuser, Kelly Johnson.
Previous CNN reports about Johnson's account referred to her only as "Kacey." CNN does not normally name alleged victims of sexual offenses, but she is being identified now because of her public testimony in court.
Johnson was the first witness to take the stand in the trial. She testified that she worked as an assistant at the William Morris talent agency from 1990 to 1996, a period in which Cosby was one her boss's most important client.
She testified that Cosby drugged her and then took advantage of her without her consent at a hotel in Los Angeles in 1996. Prosecutors introduced her testimony in an attempt to show that Cosby had a "pattern" in his assaults.
"Like Andrea, at a certain point in their friendship, he invited her over for lunch to discuss her career plans. Like Andrea, he gave her a pill. Like Andrea, she became incapacitated. Like Andrea, when she lost consciousness the defendant grabbed her hand, placed it on his penis and masturbated himself," the prosecutor told jurors.
Accuser Kelly Johnson's testimony
On the witness stand, Johnson said she became familiar with Cosby at the agency and that they would chat about her life and career plans. She called Cosby a person of "utmost importance" within the agency.
Johnson testified that Cosby would often call her "in a fatherly, favorite uncle, Dr. Huxtable type of way." She described going to Cosby's house at his invitation not long before the alleged assault. She said they acted out a scene in a script in which a tipsy woman embraces and kisses a man, which made her feel uncomfortable.
Johnson said Cosby later invited her to lunch at a hotel in Los Angeles and directed her to his bungalow. When she arrived, Cosby told her she "looked like [she] needed to relax a little bit" and offered her a large white pill, she testified.
Fighting back tears, Johnson testified that when she seemed hesitant, Cosby asked her, "Would I give you anything to hurt you?" She said she took the pill because she "felt extremely intimidated." After taking the pill, she felt like she was "underwater," she said.
She then went to the bed and Cosby laid behind her, making grunting noises, she testified. In addition, he put lotion on her hand and then made her touch his penis, she testified through tears.
Johnson said she had no more phone contact with Cosby after the incident. She testified that Cosby then put her job in jeopardy after complaining about her performance to her boss. Soon after, Johnson said, she was terminated by the agency.
Johnson described telling her parents about the alleged assault. When asked why she didn't go to the police, she said, "I was afraid. We were afraid. My father felt so powerless."
Johnson later gave a deposition about the interactions with Cosby in a workers' compensation claim about the incident at the hotel. That statement was the first time Johnson accused Cosby of assaulting her.
On cross-examination, McMonagle sharply questioned Johnson's memory of the timeline of events. Using notes from that workers' compensation deposition in 1996, he argued that her timeline had changed from that deposition to her testimony on Monday.
Johnson repeatedly said she did not recall exactly what she said in that deposition, and admitted that her memory was better at the time.
"I was bawling in that deposition and I didn't even really want to say -- I didn't want to tell anything about what happened," Johnson said.
Cosby, who has said he has vision problems, sat silently during her testimony, at times bowing his head down.
McMonagle repeatedly challenged Johnson, often interrupting her testimony. While cross-examining her, his voice often rose in pitch and became increasingly shrill, ending less with a question than implying an accusation.
A 'he said, she said' case?
Prosecutors had sought to include testimony from 13 other accusers, but District Judge Steven O'Neill ruled that would be too prejudicial.
In the deposition, Cosby said he had engaged in consensual sexual activity with Constand -- and that he had obtained Quaaludes to give them to women with whom he wanted to have sex. The unsealed deposition was central to Cosby's arrest in December 2015.
In opening statements, McMonagle launched an attack on Constand's credibility, saying she originally told police she had never been alone with Cosby before the assault, that she went to dinner with Cosby and other friends then went back to his house before the assault and that she had no contact with Cosby following the assault.
McMonagle argued that there was no dinner with friends -- Constand went to Cosby's home for career advice -- and they spoke on the phone 72 times after the assault, with Constand initiating 53 of the calls. Sometimes, they spoke for up to 40 minutes, he said.
She had also been alone with him prior to the alleged assault, the attorney said, during a visit to his Foxwoods Resort Casino hotel room in Mashantucket, Connecticut.
The prosecution countered that the defense was trying to distract jurors by talking about inconsistencies, when most of Constand's story is corroborated in Cosby's deposition.
Feden told the jury they would hear portions of a call between Cosby and Constand's mother, and said the comedian's representatives offered to fly them to Florida to discuss the matter. Cosby also offered to pay for Constand's education, which Feden painted as a concession of guilt.
"There are not a lot of facts here that are in dispute," Feden said.
The criminal complaint
In 2005, Constand, then the director of operations for the women's basketball team at Temple University, told police she had been drugged and assaulted by Cosby, a Temple alumnus who was 37 years her senior.
Sometime between mid-January and mid-February in 2004, Cosby invited Constand to his home in the Philadelphia suburbs to discuss her career plans. She told him she was "drained" and had been missing sleep, according to a criminal complaint.
Cosby gave her three blue pills, saying they would "take the edge off," according to the complaint. Cosby then offered her wine, and after some cajoling, she took a couple of sips, the complaint says.
She began experiencing blurred vision and difficulty speaking, and was "in and out," she told police. According to the complaint, Cosby positioned himself behind her on the sofa, penetrated her vagina with his fingers and put her hand on his penis. She told police she did not consent to the touching.
Cosby starred in "Fat Albert and the Cosby Kids" and "The Cosby Show." Through the latter he turned the lives of an upper middle-class African-American family into a groundbreaking TV sitcom.
His sweater-wearing portrayal of Dr. Cliff Huxtable made him a household name and one of the most beloved comedians in the world. In later years, Cosby became a public moralizer, speaking out against what he saw as the failings of African-American community in raising children.
Cosby is facing a jury of seven men and five women. Two jurors are black. The jurors will be sequestered in the criminal trial for about two weeks, the lawyers in the case have predicted.