The European Court of Human Rights has consistently reiterated that positive obligations under the European Convention on Human Rights arise when state authorities knew or ought to have known about risk of harm. This article attempts to describe and assess the role of state knowledge in the framework of positive obligations, and to situate the Court’s approach to knowledge about risk within an intelligible framework of analysis. The main argument is that the assessment of state knowledge is imbued with normative considerations. The assessment of whether the State ‘ought to have known’ is intertwined with, first, concerns that positive obligations should not impose unreasonable burden on the State and, second, the establishment of causal links between state omissions and harm.