The actors released a joint statement announcing what they are calling a trial separation.
"The reason for this separation is to better understand ourselves and the qualities we need in a partner and for our marriage," the statement said. "We remain best friends and responsible parents to our daughter and we still love each other deeply."
The statement was released shortly after In Touch Weekly reported the couple's split.
Cox, 46, and Arquette, 39, met on the set of the film "Scream" in 1996 and married three years later. They have a 6-year-old daughter together.