The European Union is increasingly moving toward an integrated policy approach, which also acknowledges linkages between public health and (external) security policy. This introduction to the Special Issue sets out a research agenda on the emerging health-security nexus. It analyses recent policy developments with respect to the public health and security, and discusses interactions along the health-security nexus in the context of the European Union. It suggests drivers behind the integrated approach and it critically examines the health-security nexus from the perspective of effectiveness and legitimacy.