The  European  Union  is  an  internal  market  where  free  movement  of  goods,  persons,  services  and  capital  is  guaranteed  by  the  EU  Treaty. Member  States  cannot  erect  or maintain  trade  barriers  in  the  form  of  regulatory  law  limiting  market  entry. Next  to  the  prohibition  of  regulatory  trade  barriers,  rules  of EU  competition law (prohibition of anticompetitive agreements, abuses of dominant  position and control of concentrations) aim at avoiding barriers to trade that are  newly created by companies wishing to protect their market position from competition. In the European Union, competition policy is practiced both on the level  of  the European Union and by  individual Member States. Competition  laws of  the Member States exist alongside the EU competition rules and, consequently,  there are also different enforcement levels. On the EU level the main actor is the  European Commission and its Competition Directorate General. Decisions of the  Commission  can  be  appealed  before  the  European  Courts.  On  the  Member  States’  level,  both National Competition Authorities  (NCAs)  and  courts  apply  rules  of  EU  competition  law. Member  States’  laws  are  enforced  according  to  national  provisions,  which  may  empower  both  administrative  agencies  and/or  courts  to apply  the antitrust provisions. The parallel  competences of  the European Commission and the NCAs may lead to coordination problems and inconsistent  enforcement  actions.  The  European  Competition  Network  has  been  created to  increase the cooperation between the European Commission and the  NCAs,  lay down  the division of work and ensure  the consistent application of  the competition rules across the EU.   Basic  principles  regarding  the  division  of  powers  between  the  European  Union and the Member States must be respected, also in the field of competition  law.  Generally,  the  EU  only  enjoys  powers  that  are  attributed  to  European authorities; some of these powers may belong exclusively to the Union whereas  others  are  shared  with  the  Member  States.  In  exercising  its  non- exclusive  powers,  the EU authorities must  respect  the principles of  subsidiarity and proportionality.3  Concerning  anticompetitive  agreements  and  abuses  of  dominant  position, the requirement of ‘impact on interstate trade’ delineates the scope of  jurisdiction with respect to anticompetitive agreements and abuses of a dominant  position. The European Commission cannot take action to prohibit anticompetitive agreements that do not have an impact on trade flows between the Member  States. However, the notion of ‘effect on interstate trade’ has been interpreted in  an increasingly broad manner by the European Court of Justice with, as a consequence, a  reduced degree of Member State autonomy.4 National competition  laws may continue to regulate anticompetitive agreements and abuses of market  power  that  generate  effects  only within  the borders  of  a  single Member State.  These laws may be similar to the European rules but, in principle, they can also  be either more or less strict than their European counterparts. Since anticompetitive …