The central aims of this dissertation were to empirically expand the extant knowledge on the extent to which OMCG membership is associated with the criminal careers of individual members, the ways in which OMCG membership is related to members’ criminal behavior, and the judicial reactions to OMCGs and OMCG membership. A multi-method approach was employed to address these research aims. The findings of the present dissertation contribute to a better understanding of the relationship between OMCG membership and crime. This dissertation suggests that OMCG membership influences the criminal careers of individual members, especially when it comes to membership of one of the most criminal OMCGs. Nevertheless, the involvement of OMCGs as collectives in members’ criminal behavior is limited: OMCGs, in most criminal cases, do not appear to orchestrate the criminal behavior to their members. OMCG membership predominantly contributes to the criminal behavior of individual members through various crime-promoting mechanisms, such as the ‘power of the patch’ and access to criminal ties. At the same time, Dutch law enforcement struggles to legally address OMCGs as criminal collectives and the symbolic contribution of fellow club members to crime through criminal law. Criminal law, after all, is primarily focused on individual liability and, therefore, has difficulties to address collective criminal behavior and criminal groups.