Fathers are more than social accidents. Research has demonstrated that fathers matter to children's development. Despite noted progress, challenges remain on how best to conceptualize and assess fathering and father–child relationships. The current monograph is the result of an SRCD-sponsored meeting of fatherhood scholars brought together to discuss these challenges and make recommendations for best practices for incorporating fathers in studies on parenting and children's development. The first aim of this monograph was to provide a brief update on the current state of research on fathering and to lay out a developmental ecological systems perspective as a conceptual framework for understanding the different spaces fathers inhabit in their children's lives. Because there is wide variability in fathers’ roles, the ecological systems perspective situates fathers, mothers, children, and other caregivers within an evolving network of interrelated social relationships in which children and their parents change over time and space (e.g., residence). The second aim was to present examples of empirical studies conducted by members of the international working group that highlighted different methods, data collection, and statistical analyses used to capture the variability in father–child relationships. The monograph ends with a commentary that elaborates on the ecological systems framework with a discussion of the broader macrosystem and social-contextual influences that impinge on fathers and their children. The collection of articles contributes to research on father–child relationships by advancing theory and presenting varied methods and analysis strategies that assist in understanding the father–child relationship and its impact on child development.