Despite the wealth of knowledge in criminological research on co-offending and peer involvement in delinquency, there is a research gap concerning the mechanisms and interactions in large peer networks. This paper addresses the latter, considering the meaning of fluctuating everyday group constellations in large networks as well as the inclusion of peers in and exclusion from offending. Fourtyfive qualitative interviews of youths who were between fifteen and twenty years old were analyzed. The findings not only suggest that delinquent and non-delinquent youths can easily coexist in large peer network but also that the everyday composition of singular groups of such networks and their interactions have a large impact on the engagement in or the avoidance of delinquency. Moreover, the data demonstrates the practice of including and excluding (non-)delinquent peers in/from offences. The insights contribute to the empirical discourse as well as the theory development on co-offending.