This chapter starts from the observation that, as far as the competitive allocation of some types of limited rights are concerned (licenses, financial grants), both EU and national legislators have not developed the relevant legal principles into more or less detailed rules yet, contrary to other types of limited rights (public contracts, sale of public assets). The central question this chapter seeks to answer is whether and to what extent these differing approaches can be rationalized. Given that a general theory is lacking, the chapter undertakes a bottom-up explanatory problem analysis of the various arguments that seem relevant for the decision of legislators to develop the principles into more or less detailed rules. The purpose of this analysis is to give a better insight into the contextual application of the various aspects that seem relevant whenever legislators consider and decide where to position the legal framework on the sliding scale between a principle-based only system, on the one hand, and a fully detailed rule-based system on the other.