Key points for reflection:

• Hierarchy of norms: certain norms are elevated due to content
• Hierarchy of sources: certain norms are elevated due to their provenance—from the source of their validity
• Norms of jus cogens: norms that, by virtue of their content, are recognised by the international community of States as a whole
• Have substantive legal effect on non-peremptory norms
• They cannot be derogated from, and may void a treaty that breaches jus cogens, or affect the obligation of treaty norms
• Obligations erga omnes: categories of obligations in which all States have a legal interest
• Not a substantive characterisation; but a procedural device to confer standing on all States
• Often map on to norms of jus cogens but can be different if provided for in a treaty (obligations erga omnes partes)