The EU Ancillary Treaties, the Vienna Convention on the Law of Treaties, and the Institutional Transformation of the EU Legal Order

The Member States of the European Union (EU), a Treaty-based International Organization, have recurrently felt the need to resort to international treaties other than the ones founding the Union itself in order to enrich the tools at their disposal in field connected with or falling within the EU areas of competence. In particular, 'ancillary treaties' have been concluded on various occasions in the field of the Economic and Monetary Union (EMU). This strategy appears useful to overcome political problems in the short term. However, the results sought with the ancillary treaties concluded in the field of the EMU could have been probably achieved (even better achieved) via instruments framed within the EU Legal order. Incorporation of such treaties in the EU legal order seems not easy at present. Moreover, it seems increasingly difficult to define what is possible under EU Law and what may be better done with ancillary treaties due in particular to political and legal ambiguities deriving from Member States.