Coherence is a powerful rhetorical device that is prevalent throughout decades of EU external relations discourse and practice. There is intuitiveness to coherence, an implied sense of ‘good fit’ between the different elements of an all-encompassing system. Yet, any attempt to concretize coherence will open up a plethora of context-specific legal and political questions. The European Neighbourhood Policy (ENP) is a recent example of an external policy drawn up explicitly with the objective of achieving coherence across different EU and Member State external policies. Positioning the ENP in the legal-historical context of political Union, this thesis first argues why coherence is an issue at all in EU external relations, and why law is integral to attaining the ever-enigmatic single voice of the European Union. Subsequently, the text examines the role of EU external relations law in attaining a coherent neighbourhood policy. It is argued that the innovative nature of the ENP for coherence lies beyond the narrowly defined legal sphere, but stems mostly from its hybrid composition of hard legal, soft legal and non-legal policy instruments. It is concluded that from a purely EU-internal and institutional perspective, this approach was reasonably successful in involving different actors towards common objectives in the neighbourhood. However, coherence should be more than rhetorical gloss, and agreeing that a wide range of initiatives should be included in soft legal instruments is no guarantee for coherence in actual policy substance. To examine the latter issue this thesis then moves beyond the realm of legal inquiry, and employs content analysis to investigate the extent to which the ENP is substantively coherent between the different norms, actors and instruments this policy encompasses.