With an eye on the changes of immense if not radical proportions that European integration has undergone in the past five years, are there any grounds for revisiting the process of flexible integration and using some of its potentials for the benefit of integration in the future? This is the main question of this article, the purpose of which, in contrast to the bulk of the literature in this field, is not so much to describe or conduct a textual analysis of the flexibility clauses of various treaties, but to understand the deeper or background reasons why flexibility in the EU has developed as it has. The article consists of three parts. The first part traces the historical development of flexible integration. This is followed by a study of the reasons why flexibility has remained on the margins of the integration process. Finally, having examined the EU’s relatively non-flexible past and the reasons for this, the focus moves to its present and future.