Active offender research relies on the collection of data from noninstitutionalized criminals and has made significant contributions to our understanding of the etiology of serious crime. This review covers its history as well as its methodological, scientific, and ethical pitfalls and advantages. Because study subjects are currently and freely engaging in crime at the time of data collection, their memories, attitudes, and feelings about their criminality and specific criminal events are rich, detailed, and accurate. Contemporary approaches to active offender research employ systematized formats for data collection and analysis that improve the validity of findings and help illuminate the foreground of crime. Although active offender research has traditionally relied on qualitative techniques, we outline the potential for it to make contributions via mixed methods, experiments, and emerging computational and technological approaches, such as virtual reality simulation studies and agent-based modeling.