This article considers the recent reform of the law to make it easier for unmarried fathers to transmit British citizenship to their children. It is suggested that this reform is interesting for the broader trends which it reflects: a movement towards formal equality between mothers and fathers, and between marital and non-marital children, and a related enhanced reliance on the genetic link as a means of grounding legal fatherhood. While the reform discussed here has received little critical attention, these broader shifts have been anything but uncontroversial in other contexts.