Recognizing that social, behavioral, and biological processes evolve over time, criminologists have been interested in how the phenomenon of crime changes over time and thus have paid close attention to developmental trajectories of crime. Several research methodologies and statistical techniques have been developed to permit study of developmental trajectories. This paper provides a non-technical overview of a method developed to examine behavioral changes over age or time-group-based trajectory modeling (GBTM). Following background material, we provide an overview of the technique. This is followed by a discussion of the applicability of the method to a variety of criminological questions, a brief review of the existing applications of the method, including the software used, as well as the advantages and disadvantages of the trajectory approach for particular questions. The paper concludes with an outline of methodological and substantive "next-steps" regarding GBTM and its application in criminology and criminal justice research.