- The first, so-called, "community pillar" placed supra-national decisions under the control of the EU Court in Luxembourg.
- The second pillar, "an intergovernmental pillar", was concerned with the area of security and foreign policy CFSP.
- The third pillar, an intergovernmental pillar", refered to the intergovernmental area of Justice and Home Affairs.
Matters within the latter two pillars were gradually shifted from the national to the supra-national level, with the result that they became gradually governed by EU law.
The Lisbon Treaty abolished the 3-pillar structure entirely. The principles of Community law established by the European Court will e.g. then also be applicable to the area of justice and home affairs.
Furthermore, as legislative community acts will be adopted in the frame of JHA, the Court will have unrestricted jurisdiction in that area.
For foreign policy the Court's jurisdiction is extended but remains limited. The Lisbon Treaty will merge the three pillars and provide the European Union with a single legal personality in Art. 47 TEU.
The EU is now a full international actor in its own right, capable of concluding international agreements with third countries and international organisations within areas where the EU has internal legislative competence (i.e. areas where the EU currently may legislate on behalf of member states).
Full text of the Treaty of Maastricht: http://eur-lex.europa.eu/en/tr......ies/dat/11992M/htm/11992M.html