Houston's publicist confirmed the singer's death to ABC News. The cause of death is not yet known.
Six police cars were spotted in front of the Beverly Hilton hotel today, where Houston was staying. TMZ reports that paramedics were called there this afternoon and found Houston unresponsive in her hotel room.
According to TMZ, paramedics' attempts at CPR failed and Houston was pronounced dead at 3:55 p.m. PT. TMZ reports that there were no signs of foul play.
Houston was last seen publicly on Thursday, when she appeared disheveled and disoriented in front of a Hollywood nightclub. According to the Hollywood Reporter, she got into an altercation with "X Factor" finalist Stacy Francis on Thursday at an event where she was said to be acting "belligerent."
Houston returned to rehab in May of last year seeking treatment for drug and alcohol dependence. "Whitney voluntarily entered the program to support her long-standing recovery process," her publicist said at the time.
The six-time Grammy winner staged a comeback in 2009, but was dogged by rumors that she was using drugs again. That year, she told Oprah Winfrey that marijuana laced with cocaine was her substance of choice during her 1992 to 2006 marriage to R&B singer Bobby Brown. They have a daughter together, Houston's only child, Bobbi Kristina Houston Brown.
Houston's appearance on "Oprah" was her first major television interview since 2002, when she talked to ABC News' Diane Sawyer.
At the time, Sawyer asked Houston about ongoing drug rumors that had started in 2000, when airport security guards found marijuana in Houston and Brown's bags at a Hawaiian airport. The singer alluded to having used cocaine, pills and marijuana -- but drew the line at crack in what turned into an infamous rant.
"First of all, let's get one thing straight," she told Sawyer. "Crack is cheap. I make too much money to ever smoke crack. Let's get that straight. OK? We don't do crack. We don't do that. Crack is wack."
In August 2009, Houston released "I Look to You," her first studio album in seven years. It sold 304,000 copies in its first seven days on the market, sending Houston back to the top of the charts and giving her the best debut week of her career.
In 2010, Houston launched her "Nothing but Love" world tour. Though some said Houston's signature voice showed the stress of her ups and downs, she soldiered on, putting on shows in Asia, Australia and Europe even though fans and critics panned her performances.
At her peak in the 1990s, Houston was a force to be reckoned with in the music industry. She was one of the world's best-selling artists, selling out stadiums with powerful, poignant renditions of her greatest hits like "I Wanna Dance With Somebody," "How Will I Know," and "I Will Always Love You."
Houston won six Grammy awards, two Emmys, 30 Billboard Music Awards, and 22 American Music Awards, among others. Her album "Whitney" was the first album by a woman to ever debut at No. 1 on the Billboard Charts. She has sold more than 170 million albums world wide.
Her success launched her into the film industry, where she starred in hits like "The Bodyguard" and "Waiting to Exhale." Her struggles with drugs, alcohol, rehab (she went at least three times) and Brown, against whom she filed a charge of domestic abuse in 1993, pushed her out the spotlight.
In 2009, talking to Winfrey about why she took a break from show business, Houston said, "It was too much. So much to try to live up to, to try to be, and I wanted out."
The Associated Press contributed to this report.