On 23 July 2025, the International Court of Justice (ICJ) rendered, unanimously, a landmark Advisory Opinion on the Obligations of States in Respect of Climate Change. In doing so, it placed the right to health at the centre of the international legal response to the climate crisis: States’ climate conduct is now assessable against human rights criteria, and climate inaction is no longer merely a political failure but may become a legal one with identifiable consequences. This policy brief explains what the Court decided and why it matters for global health actors. It sets out the obligations identified by the Court (Section 2), the legal consequences that flow from their breach (Section 3), and the practical implications for the World Health Organization (WHO) and the World Health Assembly (WHA), health law instruments, international institutions, and litigation (Section 4), before drawing conclusions on the accountability era the Opinion may inaugurate (Section 5).