The stepparent relationship provides a source of potential conflict in remarriage families, since the biological parent and stepparent may have different interests in the well-being and even survival of children from the wife's prior union. From an evolutionary perspective, there are circumstances in which stepparents benefit from providing care for and investments in their stepchildren, and circumstances in which they do not. From a sociological perspective, ambiguity and incomplete institutionalization provide little guidance for stepparents in managing these complex living arrangements, which may lead to equal investment in all children, regardless of relationship. Men who take on the stepparent role may be selected for either negative or positive characteristics. This paper compares parenting patterns of residential fathers in two-biological-parent, married-stepparent, and cohabiting father-figure families to see whether there are systematic differences in paternal investments in these types of families. The data come from 2,531 children and their parents who were interviewed during the 1997 wave of the Child Development Supplement to the Panel Study of Income Dynamics. Results support the incomplete institutionalization hypothesis and positive selectivity in that differences in investments are small in families with both biological children and stepchildren, and stepchildren benefit substantially from being in this family type.