European Court of Human Rights – Subsidiarity – Margin of appreciation – Deference – Theorising the margin of appreciation based on a large case law study – The ‘systemic’ (rethought ‘structural’) element of the margin of appreciation relies on a functional rationale related to the distribution of tasks within the European system for the protection of human rights and is based on non-merits reasons – The ‘normative’ (rethought ‘substantive’) element reflects normative flexibility and is based on merits reasons – Both margins reflect the principle of subsidiarity – The two margins most often interact in partial deference but the systemic margin can also lead to complete deference – Presumptions of complete deference in the case law of the Court – Implications of increased reliance on the systemic margin as the Court moves emphasis from ‘substantive’ to ‘procedural’ review.