An estimated 15 million mothers with young children in the U.S. suffer from depression. Untreated maternal depression has serious consequences for the mother's long-term health and for her child's development and functioning. it can also be costly, driving up health care use, reducing employment, and creating the need for early childhood interventions. Treatments for depression, usually combining medication and psychotherapy, have been proven effective in the general population, but there is limited evidence for how much they help mothers and for their cost-effectiveness. Stronger evidence about what works in treating maternal depression, and the value of alternative treatment options, could inform best practices and improve the lives of millions of mothers and children.