Abstract
National healthy cities networks (NNs) were created 20 years ago to support the development of healthy cities within the WHO Europe Region. Using the concept of epistemic communities, the evolution and impact of NNs is considered, as is their future development. Healthy cities national networks are providing information, training and support to member cities. In many cases, they are also involved in supporting national public health policy development and disseminating out healthy city principles to other local authorities. National networks are a fragile but an extremely valuable resource for sharing public health knowledge.