The couple started dating in 2006 and are the parents of a 2-year-old son.
"We remain friends and deeply committed and loving parents to our son Bronx, whose happiness and well-being remains our No. 1 priority," Simpson-Wentz and Wentz said in a joint statement Wednesday.
"Ashlee loves Bronx but jumped into marriage and having a baby too quickly," one source told UsMagazine.com. "They feel they got trapped in a situation they were too young for."