This paper addresses the challenge of achieving an appropriate balance between
unity and diversity within multilevel constitutional systems. It proposes a parallel
examination of two theoretical frameworks: differentiation in EU law and
asymmetric federalism. Although the principles of unity and effectiveness are
central to the EU legal order, differentiation has consistently featured in the
evolution of European integration. Through various mechanisms of differentiation,
the EU has managed the increasing diversity among its Member States.
Similarly, (quasi-)federal systems tackle this issue by introducing various forms
of asymmetries, which are analysed within the framework of the theory of
asymmetric federalism. The paper demonstrates significant overlap between
differentiation in EU law and asymmetries in (quasi-)federal systems in terms
of their causes, explanations, outcomes, and normative foundations. Investigating
multilevel constitutional systems through the simultaneous use of differentiation
and asymmetric federalism facilitates the achievement of explanatory,
analytical, and normative objectives. Specifically, this paper focuses on the relevance
of employing asymmetries in the EU, thereby presenting an innovative
approach to addressing the challenge of diversity in multilevel systems.
Key words: multilevel constitutional systems, accommodation of diversity,
differentiation, European Union, asymmetric federalism, (quasi-)federal systems,
unity, diversity.