The group in criminal law puts the problem of the apprehension and the repression of the collective crime and participants' plurality in the malpractice, whatever can be its demonstrations ; these works so have for ambition to replace the various apprehensions of the group in a linear step, and want systematism. So as it will be attempted to loosen a certain cohesion in front of the visible dispersal of our repressive arsenal. It is a question of connecting the various perceptions of the group and of following the progress, so many criminological realities that social reactions. In the alder of this systematic approach of the group, are measured, in terms of opportunity, critics, evaluation positive and forward-looking, the various penal perceptions of the group, that the social reaction is ex ante, or ex post. The group appears at first as measuring instrument of the crime in power, then as a revelation of the crime in action. The repression follows a dynamics of extension, directed to the repression of the biggest attendance figures.