The ever incomplete single market: differentiation and the evolving frontier of integration

Progress in market integration over the past two decades has come at
the expense of growing flexibility in the laws that govern the singlemarket (SM) as well
as the way that these laws are implemented. This differentiated integration comes
in four forms: soft; informal; multi-speed; and opt-out differentiation. We examine
how the completion of the SM has been held back in the varied implementation of
EU competition policy and variation in national corporate law, energy markets,
services and taxation. These sectors and issue areas form the frontier in which the
main political struggles over the future shape of the SM take place, and in which differentiation
is most clearly manifested. The SM notion supposedly entails a concrete set
of substantive policy commitments that form the basis of the ‘ever closer union’.
However, increasing differentiation undermines the identification of the EU’s core
constitutional commitments.