This article looks at the first phase of the implementation and application of the EU-Ukraine Association Agreement, which triggered unprecedented political, economic and legal reforms in Ukraine. In particular, the article focuses on the constitutional challenges that have arisen for Ukraine in the course of implementing the Association Agreement into its legal system. Two issues form the focus of consideration in the article. The first issue is effective implementation and application of the Association Agreement within the Ukrainian legal order. The second issue is compatibility between the Association Agreement and the Ukrainian Constitution. The latest political and legal developments in Ukraine are analyzed through the prism of effective implementation of the Association Agreement and the rise of pro-European judicial activism in Ukraine. In conclusion it is argued that the EU-Ukraine Association Agreement enhanced the adaptability of the national constitutional order to the European integration project and European common values.