"Melissa and Tammy Etheridge are saddened to announce that they are now separated," Melissa's rep told the magazine.
A statement from the couple added, "We ask for consideration and respect for our family as we go through this difficult period."
Melissa, 48, and Tammy (formerly Tammy Lynn Michaels), 35, exchanged vows in Malibu, Calif., in 2003. Tammy gave birth to twins - son Miller and daughter Jonnie Rose - in 2006.
Melissa is also mother to children Bailey, 13, and Beckett, 11, with former partner Julie Cypher.