According to court documents obtained by ET, the 38-year-old actress is seeking spousal support, as well as joint legal and physical custody of their two sons - 12-year-old IN and 9-year-old Atticus.
The couple previously announced their separation in March 2016, but an unknown fact about their split came out with the divorce news this week.
Casey and Summer went on to become a couple in 2000, got engaged in 2003 and got married in June of 2006.
Casey and Summer were introduced to each other by the latter's brother in the mid-1990s.
Actress Summer Phoenix brought her petition in Los Angeles Superior Court. In 2001, they both performed in the play This Is Our Youth with Matt Damon, another member of the Affleck pair's inner circle. They have two sons, Indiana August and Atticus. She is also seeking spousal support. A rep for Affleck told E! at the time the split was friendly.
Since then, Casey has displayed with Floriana Lima... especially for the Oscars. They Wednesday in June, 2006 following the birth of their first child. Back in 2010, he was sued by two of his former co-workers for more than $2 million.