EU competition law provisions are worded in broad and vague terms. As a result, they are fleshed out from the bottom up through their case-by-case application to concrete scenarios. This chapter identifies, first, the choices that courts authorities make when giving content to competition law provisions. Practices may be subject to a rule or a standard. Under the first, the practice is deemed prima facie lawful or unlawful irrespective of its impact. Under a standard, the legality of the conduct depends on a case-by-case assessment of its effects. The chapter identifies the various approaches to the divide between rules and standards and the different meanings that can be given to the notion of effects. Concerns with due process and undue deference are often raised by commentators. However, there is a tendency to ignore that these concerns have a substantive dimension: over time, due process and undue deference can be expected to impact on the substantive dimension of the field, in that they can be expected to make the law less consistent and less predictable. This is the background against which the analysis in the monograph is conducted. This chapter maps the factors that may influence the behaviour of the European Commission and the EU courts in one-shot and repeated interactions.