This chapter starts with an theoretical exploration of the nature of computerized practices of Law application. Then four generations of Law are identified in which the last generation can be understood as a form of legal mass customization. Characteristic for this fourth generation law is interactivity at a large scale. The theoretical discussion of the control of large-scale computerized policy implementation is illustrated by a case study of the use of large-scale information systems in Dutch and European immigration policies. It is argued that modern, western states, need a type of power that forms an addition to the existing Trias Politica. This because the Trias Politica is falling short on its promise of providing a check on the application of law because the fourth generation law offers the legislating power new instruments to limit the power of judges and the administration. As a result, there is no formal power which is concerned with supervising and correcting of the large scale exertion of power. As a way to restore the necessary balance of power a Tetras Politica is suggested.