The main aim of the article is to point out and assess the modifications introduced by the Treaty of Lisbon in respect both to the present legal situation and to the solutions proposed in the Constitution for Europe. The authoressess undertake a task to evaluate the real 'reforming value' of the Lisbon Treaty. To avoid associations with the Constitutional Treaty, it was decided to retain the structure of two treaties: Treaty on European Union and Treaty on functioning of the European Union instead of replacing them by one Treaty. The European Union will replace and succeed the European Community, thus becoming a coherent international organization equipped with legal personality. One of the consequences of this fundamental change will be the suppression of the three pillar structure of the EU, established in the Treaty of Maastricht. The paper examines modifications introduced by the Lisbon Treaty in the following fields: the protection of fundamental rights; the future Common Foreign and Security Policy, the Area of Freedom, Security and Justice, institutional changes; the role of national parliaments, as well as changes brought to the substantial EC law.