Policy networks can help to coordinate different objectives. The vast literature on network governance often implies that the mere existence of networks will automatically lead to improved coordination. However, much empirical analysis so far has focused on networks within particular policy sectors, which may actually inhibit horizontal coordination across policy sectors. This focus has led to ambiguities regarding the use of networks in practice — which this article seeks to help address. By analysing the role of networks in the coordination of the EU’s economic and environmental objectives in the development of its mercury policy, the article demonstrates that policy networks need to span several policy sectors if they are to help reconcile competing policy objectives. Furthermore, certain characteristics of the policy area which contributed to the formation of an inter-sector network in this case are discussed.