There are obvious tensions in the relationship between horizontal and flanking policies, such as environmental, consumer, public health and cultural policies, and the EC rules on free movement and competition. An explanation:- The application of the EC Treaty provisions on the four freedoms set limitations to national competence in the field of horizontal and flanking policies. - The application of the EC rules on competition entails that both Member States and private parties are limited to enact measures with horizontal and flanking policy objectives, but with anti-competitive consequences.- Community legislature can put in place harmonisation measures to remove the existing tensions. But these measures must also be in conformity with the Treaty provisions on the four freedoms.These three sources of tension are thoroughly analysed in this study on the basis of the case law of the European Court of Justice, the decision practice of the European Commission in competition cases and Community harmonisation measures in the fields of the environment, consumer policy, public health and culture. From the perspective of both the Member State and the Community, would it be possible to really attain closer harmony between free movement, competition and horizontal and flanking policies? What can national bodies such as the national legislature, the national competition authority and the national court, and Community bodies, in particular the European Court of Justice, the European Commission and the Community legislature do to control and ultimately resolve this problem of tension? In the end, would it not be better to re-organise and re-define the EC Treaty in respect of horizontal and flanking policies? This study aims to answer these and other questions.Tensions within the Internal Market