The healthcare system accounts for 5 to 8% of greenhouse gas emissions. Since the 2010s, several institutions have been calling on healthcare systems to reduce their carbon footprint without compromising the quality of care. This article describes an ecological transition process in healthcare at the Geneva University Hospitals, in the form of a certification program for "eco-care" units, driven by frontline professionals' commitment to human and planetary health, comprising both an educational and an operational component. The certification process mobilizes units around a shared transition project and aims to transform the culture and standards of care throughout the entire healthcare institution.