Aniston, 35, and Pitt, 41, began dating in 1998 and were married in July 2000. Recently, though, Aniston was photographed not wearing her wedding ring, leading to reports of discord.
"We happily remain committed and caring friends with great love and admiration for one another," the couple said in a statement to People magazine, which first reported the split on its Web site late Friday.
"This decision is the result of much thoughtful consideration," and is not "the result of any of the speculation reported by the tabloid media," the high-profile pair said.
News of the separation surprised some, who noted that the couple spent New Year's together on the Caribbean island of Anguilla, where they were photographed in affectionate poses.