The European Union is based on the rule of law. Every action taken by the EU is hence based on a legal framework, namely the treaties that all member states have approved freely and democratically. Therefore, the EU can only take action in the areas where it has legal authority. The current treaty framework, the Lisbon Treaty, defines the areas in which the EU has full authority  to make decisions, those in which the competences are shared between the EU institutions and the member states and those in which only the member states have a say.

A treaty is a binding agreement between the European Union and the member states, defining the rules under which the EU works, its obligations, the way decisions are made and the relationship between the institutions and the member states. 

In the history of the European Union, treaties have been amended in order to adapt to changes such as an enlargement of member states and the inclusion of new competences to the EU authorities or improve efficiency, transparency, and democracy.

Overview of the Treaties