Evidence regarding whether fathers are “essential” for or contribute substantially to children’s development over and above their financial contributions is still emerging. The question of how exactly fathers matter for children’s development has dominated much of the emerging research on fatherhood and has produced some promising findings. In this chapter, I briefly review the theoretical underpinnings of what fathers do and how it matters for children’s development. I then examine current findings on the association between fathers’ involvement and children’s outcomes over time, and conclude with suggestions for future research.