Public sector inter-organisational information sharing and interoperability is an area of increasing concern and intense investment for practice and an area of increasing scholarship. This paper focuses on one particular set of public sector organisations (emergency services) and illuminates the key technological and organisational issues they face concerning information sharing and interoperability. The particular contexts in which these are studied are ones where decisions are non-trivial and made in high-velocity environments. In these conditions the problems and significance of inter-organisational information sharing and interoperability are accentuated. We analyse data gathered from two studies: the first focused on ‘first responders’ (police, fire and ambulance services) in the United Kingdom. The second, a follow on study, with emergency service managers and interoperability project managers in the United Kingdom and the European Union. Using activity theory as a conceptual framework we describe the informational problems critical emergency responders face in their initial response to, and management of, an incident. We argue that rather than focusing on interoperability as a primarily technological issue it should be managed as an organisational and informational issue. Second, we argue that rather than designing for anomalous situations we should design systems, which will function during both anomalous and routine situations. Third, we argue for focus on harmonisation of policies, procedures and working practices.