Healthy Ageing is an important focus of the European Healthy Cities Network and has been supported by WHO since 2003 as a key strategic topic, since 2010 in cooperation with the Global Network of Age-friendly Cities and Communities. Based on the methodology of realist evaluation, this article synthesizes qualitative evidence from 33 structured case studies (CS) from 32 WHO European Healthy Cities, 72 annual reports from Network cities and 71 quantitative responses to a General Evaluation Questionnaire. City cases are assigned to three clusters containing the eight domains of an age-friendly city proposed by WHO's Global Age-friendly City Guide published in 2007. The analysis of city's practice and efforts in this article takes stock of how cities have developed the institutional prerequisites and processes necessary for implementing age-friendly strategies, programmes and projects. A content analysis of the CS maps activities across age-friendly domains and illustrates how cities contribute to improving the social and physical environments of older people and enhance the health and social services provided by municipalities and their partners.