With hindsight, the Maastricht Treaty introduced two different forms of flexibility or differentiated integration. The Social Protocol took the form of a permission by all the Member States to a group of Member States to use Community institutions and legislation, which can be seen as the precursor of the general provisions on “closer cooperation” in the Amsterdam Treaty. On the other hand, the provisions on Economic and Monetary Union provide for some Member States to receive opt-outs or derogations from binding Treaty obligations and thus provide the model for the new Title of the EC Treaty on visa, asylum and immigration introduced by the Amsterdam Treaty.
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