The 49-year-old actress released a statement via her publicist saying: "It is with great sadness and a heavy heart that I have decided to end my six-year marriage to Ashton.
"As a woman, a mother and a wife there are certain values and vows that I hold sacred, and it is in this spirit that I have chosen to move forward with my life.
"This is a trying time for me and my family, and so I would ask for the same compassion and privacy that you would give to anyone going through a similar situation."
Just minutes later Ashton tweeted: "I will forever cherish the time I spent with Demi. Marriage is one of the most difficult things in the world and unfortunately sometimes they fail. Love and Light, AK."
Demi and Ashton married in September 2005 and have come under intense scrutiny over the last two months, when Ashton was accused of cheating on Demi on the eve of their sixth wedding anniversary.
The couple were surrounded by split rumours at the end of September, when Sara Leal claimed she slept with Ashton after partying together in San Diego.
The 33-year-old actor seemed to respond to the claims by tweeting a link to what he was playing on Spotify: "Don't Believe The Hype" by Public Enemy, and later tweeting the quote: "'When you ASSUME to know that which you know nothing of you make an A** out of U and ME.'"
Ashton faced rumours of flings before, when 21-year-old Brittney Jones claimed she had a one-night stand with the ‘Two And A Half Men’ actor last year.
Demi’s weight plummeted in the weeks following the accusations, and the couple did not attend any public appearances together, but were spotted together attending their Kabbalah centre.
We hope Demi and Ashton both get through this tough time.