This article looks upon the most recent developments in the European Union’s accession strategies, as from the start of accession negotiations. It first seeks to demonstrate that the pre-accession conditionality rationale of stabilising present and protecting future integration objectives underpins the so-called ‘specific safeguard clauses’ of the 2003 and 2005 Acts of Accession and the latter’s cooperation and verification mechanism, accordingly referred to as post-accession conditionality tools. It then argues that this rationale, emphasised also in the imperative of maintaining the momentum of European integration of the Union’s ‘integration capacity’, above all necessitates effective compliance with EU law, and thus full administrative and judicial capacity of (prospective) Member States. Indeed, the lynchpin of these new conditionality devices evokes putting them in the wider context of compliance mechanisms in the enlarged European Union. It thereby becomes apparent how conditionality has lead to a considerable empowerment of the European Commission which, when reaching into the post-accession phase, entails a problematic differentiation between the Member States. Conditionality methodology furthermore, and this is equally shown, has had an impact on the Commission’s role as ‘guardian of the treaty’ within the overall system of ensuring compliance with EU law.