Gwen cites irreconcilable differences in her divorce petition, which seeks to end their 13-year-marriage.
Gwen, who's repped by attorney Scott Weston, is asking for joint custody of the couple's 3 kids -- 9-year-old Kingston, 6-year-old Zuma and 1-year-old Apollo.
Gavin, who's repped by disso-queen Laura Wasser, filed his response at the same time, and he's also asking for joint custody. It's clear the petition and response were orchestrated to be filed simultaneously.
Sources tell TMZ there is no prenup, so the 50/50 California community property laws kick in. 45-year-old Gwen is worth a reported $80 million, and 49-year-old Gavin's worth an estimated $35 million. Given the length of the marriage, that will probably all go into one pot before it's divided.
Gwen checked the box on the form to deny Gavin spousal support.
In a joint statement they said, "While the two of us have come to the mutual decision that we will no longer be partners in marriage, we remain partners in parenthood and are committed to jointly raising our three sons in a happy and healthy environment."