This chapter presents 10 years of research into a developmental taxonomy of antisocial behavior that proposed two primary hypothetical prototypes: life-course-persistent versus adolescence-limited offenders. It suggests that life-course-persistent antisocial behavior originates early in life, when the difficult behavior of a high-risk young child is exacerbated by a high-risk social environment. The Dunedin findings about differential neurodevelopmental and family risk correlates for childhood-onset versus adolescent-onset offenders are generally in keeping with findings reported from the samples. It would be useful to ascertain the genetic and environmental architecture of individual differences in trajectories of antisocial behavior over time. The original statement of the taxonomy asserted that the theory describes the behavior of females as well as it describes the behavior of males. Other findings have pointed to important revisions needed to improve the fit between the taxonomy and nature, and some findings raise serious challenges to aspects of the taxonomy.