The mechanism established in what has now become Article 352 of the Treaty on the Functioning of the European Union (formerly known as Article 235 and 308) has many names. One of the more common is to refer to the mechanism as the 'flexibility clause'. As the notion indicates, the basic purpose of the mechanism is to provide the European Union with a possibility of (flexibly) adjusting legislative powers to arising needs. Since the very purpose of the flexibility clause is to provide for the exercise of legal powers where none is to be found in the EU Treaties, the clause hereby defines the ultimate reach of EU competence. Remarkably, although use of the clause has often been contentious, the wording of the clause has remained unchanged ever since the Treaty of Rome. The aim of the article is to outline the function and development of the flexibility clause especially in light of the Treaty of Lisbon, which for the first time in the history of the EC/EU rewrites the flexibility clause.