Many abstractions of program dependences have already been proposed, such as the Dependence Distance, the Dependence Direction Vector, the Dependence Level or the Dependence Cone. These different abstractions have different precision. The minimal abstraction associated to a transformation is the abstraction that contains the minimal amount of information necessary to decide when such a transformation is legal. The minimal abstractions for loop reordering and unimodular transformations are presented. As an example, the dependence cone, that approximates dependences by a convex cone of the dependence distance vectors, is the minimal abstraction for unimodular transformations.