Ever more detailed European Environmental legislation makes it increasingly necessary to see the system as a whole. A consistent and coherent structure is suggested as an important element of successful regulation. The paper sets out a conceptual framework for studying the conditions under which coherence could be confirmed. Coherence is proposed as a legal principle within EU (Environmental) Law with an imperative to act in favour of this principle. Using the primary EU law and general EU legal policy for analysis, the design of the paper is deductive: Bearing in mind the concept of coherence within the Good Governance and Better Legislation initiatives, the paper suggests coherence not only as a rule but as a legal principle in EU law and explores the consequences of such a shift. The paper shows that coherence has the capacity to improve environmental regulation until restrained by concepts of subsidiarity and proportionality. The main findings concern the specific commitments of this normative approach in the EU Environmental Law, by focussing on the new Commission Directive on Industrial Emissions (IED) as the central regulation of industrial plants. The findings suggest that the IED is some distance away from an optimal coherent status.