The Multi-site Family Study on Incarceration, Parenting and Partnering (MFS-IP) was an evaluation of federal family strengthening programs for incarcerated and reentering fathers and their partners, which has produced the field’s richest quantitative dataset for understanding the experiences of these families. In 2006, the U.S. Department of Health and Human Services (HHS), Administration for Children and Families (ACF), funded an initiative to support healthy marriage and responsible fatherhood. Thirteen grantees in 12 different states received five-year grants from the ACF's Office of Family Assistance to implement multiple activities to support and sustain marriages and families of fathers during and after incarceration. To evaluate the overall effectiveness of the 13 MFS-IP grantees, RTI conducted an implementation evaluation and a multi-site, longitudinal, impact evaluation of selected grantees. The evaluation was designed to add to research, policy, and practice by helping to determine what types of programs work best for those involved in the criminal justice system, what does not work, and what effects these programs may have on fostering healthy relationships, families, and children. The study team was also able to generate a stronger understanding of the experiences of justice-involved families before, during, and after a father's incarceration.