Free movement of goods, one of the ‘four freedoms’ together with free movement of persons, services, and capital covered in the Treaties, is a fundamental principle with two purposes. The first is purely economic; a customs union and common market comprising individual Member States cannot be established unless goods from all the Member States are sold freely and compete effectively in all the Member States. The second is political, if there is to be a single common market then goods must flow freely within its borders. The effect of national measures that block the importation of goods from one Member State to another, make their marketing more difficult, or raise their price, is the distortion of the free flow of goods and competition. Inevitably, in a single market such measures have to be eliminated.