Criminal groups have traditionally been the focus of criminological research because of the collective dimension of many criminal activities or deviance. However, what constitutes a ‘criminal group’ or how specific criminal groups, like gangs, should be defined, remains open for discussion in the scientific literature. This introductory article highlights a number of recent developments illustrating the blurring boundaries between various criminal groups as defined by both insiders and outsiders. In addition, it suggests that the rise of social media and smartphones is changing the structure and dynamics of criminal groups. Future research should focus on how these (new) criminal groups originate, develop and function, but should also address the role of the group in criminal activities.