Parental leave, a key aspect of family policy, is a relatively new concept in the United States; it is crucial that policy development be guided by social science research. In this article we first review policy issues associated with parental leave. Following that, we consider relevant social science research pertaining to parental leave and mothers' and fathers' functioning (e.g., mental health, relationship with spouse and infant). We focus particularly on results emerging from the Wisconsin Maternity Leave and Health Project, which suggest, for example, that short leave (6 weeks or less) for women is a risk factor, when combined with other risk factors such as marital concerns, for depression. We conclude with policy implications of this and related research.