Group-based analysis of developmental trajectories has been commonly used to study heterogeneity in criminal offending over the life course. While there have been several critiques of this method, we believe that it is useful in testing hypotheses from theory about the existence of groups and the characteristics and attributes of groups. We present an overview of these issues and close with two points. First, since criminology owes much to description, the group-based method offers one method that permits visualization of data and connection of what we see to the data. Second, although the group-based model is a useful descriptive tool, it is not a mere descriptive tool, as it can be used to test empirical predictions from theory, including the predictions of non-taxonomic criminological theories, as well as other fundamental criminological/criminal justice questions.