Until now my work has focused on the social construction of ageing, at the meeting point between knowledge and public policies. My thesis explored outplacement of unemployed older adults (45) as a case of (then) new activation policies (‘active ageing in employment’), suggesting that it might be seen as a ‘new government of the end of careers’, placing more responsibility on individuals. As part of my first post-doctorate at Belgium’s National Scientific Research Fund (FRS-FNRS) and a period at King’s College, London, I broadened my focus by showing the key role played by International Organizations (European Commission, Organization for Economic Cooperation and Development, Word Health Organization, United Nations) and English-speaking researchers in the plural definitions of active ageing beyond employment. Shifting my attention to the challenges of social participation and citizenship supported by such international discourses, I looked at the emergence and spread of ‘age-friendly cities and communities’ worldwide. In the course of a second post-doc mission as the scientific coordinator of a three-year study programme at the International Network for Study of Age, Citizenship and Socio-economic Integration (Reaictis, Dijon), I observed the spread of various schemes for senior citizenship in a dozen cities in Belgium, Spain, the United States, France, the United Kingdom and Quebec province, Canada, as well as the way these schemes interacted with ‘age-friendly cities and communities’. Since 2012, I also have been observing how the Walloon Government in Belgium has adopted such approach and to what extent it promotes innovation in social theory and practice with regard to ‘community building’. Finally ageing remains a key tool for conceptualizing relations between knowledge and action without the two poles being insulated from one another.