Abstract Issue/problem Gambling represents a public health, social, and economic problem. Lombardy Region, according with national and regional law, has approved the Regional Plan for the prevention and contrast of Pathological Gambling. The Health Protection Agencies (HPA) of the Metropolitan City of Milan, as the other HPAs, implemented the Local Gambling Plan, based on a context analysis and in synergy with all the actors involved. Description of the problem Since 2019, the Milan HPA’s Local Gambling Plan has been implemented through collaboration with non-profit entities (TSEs), which are involved via public tendering. The implementation of the new Italian ‘Code of the Third Sector’ changed the TSEs engagement modalities. For this reason, a complex co-planning process has been initiated in order to increase the level of active citizenship and to enhance public health, in line with horizontal subsidiarity principle. Results The Co-planning procedure promoted the integration among local health services, non-profit entities and municipalities with the aim of gambling prevention and contrast, ensuring the continuity of prevention programs and the involvement of local stakeholders in addressing a public health issue. During the co-planning, 9 working groups were established to define objectives, project actions, monitoring and evaluation methods, ensuring the common interest of all actors involved. Lessons For the health and social system, the co-planning procedure becomes an opportunity to translate what is foreseen by the regulations into local actions. It allow the active participation of local stakeholders involved into the co-construction and achievement of public health objectives and the promotion of communities’ empowerment. Key messages • Co-planning is both a process and a tool for local welfare. • Co-planning involved multiple actors, among which the public institution that ensures satisfaction of health needs through governance actions.