International audience ; Based on a reflexive method, this article explores the roles of researchers behind Age-Friendly Cities and Environments. Referring to Michael Burawoy's division of sociological work (professional, critical, policy and public sociology), it is structured around the international comparison of two empirical case studies: Walloon region (Belgium) and Quebec (a province of Canada). While the first case shows some difficulties faced by a limited policy sociology perspective with little room for research, the latter presents a more developed public sociology approach with larger involvement from research. If both cases started with policy links, the latter presents a special interest for praxis, through knowledge transfer as an ongoing public dialogue. Based on this comparison, the article concludes with a twofold use of praxis: on one side – knowledge in action – a public sociology position offers an original perspective on what AFC/AFE may mean and produce to avoid a limited field of actions focusing only on some stakeholders or advocates for older people. On the other side – action in knowledge – policy and public sociology question professional and critical sociology facing AFC/AFE programmes: is a purely academic knowledge of such a programme epistemologically realistic or should it necessarily be empirically fuelled?