Does subsidiarity apply to all international treaties or just EU law?

Question

I'm trying to understand if the principle of subsidiarity, as referenced in the European Convention on Human Rights (ECHR), applies to all international law or if it's specific to EU law. Could someone clarify the general applicability of this principle across different treaties and international frameworks for me?

James L. Arrasmith · Answer

The principle of subsidiarity extends beyond EU law, though it has become most prominently associated with European Union governance. You'll find this concept deeply embedded in EU treaties, where it guides decision-making between Union-level and member state actions. 
 
In broader international law, subsidiarity operates more as an interpretive principle rather than a strict legal requirement. When you examine treaties like the ECHR, you'll notice subsidiarity manifests through the "margin of appreciation" doctrine, which respects national authorities' discretion in implementing human rights obligations. This reflects the understanding that local bodies often know best how to address their specific circumstances. 
 
Think of subsidiarity as a flexible guideline that helps determine the most appropriate level for decision-making across different legal frameworks. While the EU has formalized it extensively, other international organizations and treaties may incorporate subsidiarity principles less explicitly. For example, the UN system generally respects member states' primary responsibility in domestic matters, intervening only when national mechanisms prove inadequate. This demonstrates how subsidiarity's core idea - that governance should happen at the most effective level - resonates throughout international law, even when not explicitly labeled as such.

Q: Does subsidiarity apply to all international treaties or just EU law?