Special prosecutor Angela Corey announced the charge at a news conference Wednesday, seven weeks after the homicide took place.
Trayvon Martin's parents, civil rights leaders and other people have portrayed the case as racially charged, saying Zimmerman would have been arrested immediately had he been black and the victim white. Martin was black.
The case has raised a multitude of questions, some of which remain unanswered.
Q: WHY DID IT TAKE SO LONG FOR ZIMMERMAN TO BE ARRESTED?
A: Special prosecutor Angela Corey says that probable cause had to be determined before authorities could arrest Zimmerman. She said there was only a slight delay, when she took it over from the previous prosecutor, who recused himself from the case.
Zimmerman told police he acted in self-defense after Martin pursued and attacked him. Florida is among 21 states with a "stand your ground law," which gives people wide latitude to use deadly force rather than retreat during a fight. The Florida law lets police on the scene decide whether they believe the self-defense claim.
In many cases, the officers make an arrest and leave it to the courts to work out whether the deadly force is justified. In this case, however, police have said they are confident they did the right thing by not charging Zimmerman.
Q: ON WHAT EVIDENCE IS THE PROSECUTOR BASING THE CHARGE OF SECOND-DEGREE MURDER?
A: Corey did not disclose how she arrived at the charge, saying that was information to be revealed in court.
Q: WHAT'S NEXT?
A: Zimmerman will appear in court within 24 hours, Corey said.
Q: DOES ZIMMERMAN HAVE LEGAL COUNSEL?
A: Yes, Mark O'Mara of Orlando, who became Zimmerman's new attorney after his former lawyers announced Tuesday that they were dropping the case. They said they couldn't keep representing Zimmerman because he had stopped communicating with them.
Q: WHAT HAPPENED?
A: Martin, 17, was shot and killed by a single gunshot wound to the chest Feb. 26 during a confrontation with Zimmerman, a 28-year-old neighborhood watch volunteer in a gated community of townhomes in Sanford, Fla., about 20 miles northeast of Orlando.
Zimmerman was driving through the neighborhood when he spotted Martin, who was unarmed and walking to the home of his father's fiancee. She lived in the same gated community as Zimmerman.
Martin was returning from a trip to the convenience store with an iced tea and a bag of Skittles. It was raining, and Martin was walking with the hood of his sweatshirt pulled over his head. He talked to his girlfriend on a cellphone moments before the shooting, according to Martin's family's attorney.
Q: WHAT IS GEORGE ZIMMERMAN'S SIDE OF THE STORY?
A: On his website, therealgeorgezimmerman.com, Zimmerman has described the shooting as "a life altering event" but he says he can't go into details about what happened.