The 1992 UN Conference on Environment and Development, the Rio Earth Summit, gathered an unprecedented number of heads of state and produced Agenda 21, a comprehensive action plan for sustainable development, alongside framework conventions on climate change and biodiversity. Agenda 21 assigned a central role to local government, calling on municipalities to develop 'Local Agenda 21' strategies through community participation. It connected environmental protection with economic and social development. The summit popularised sustainability as a governing concept.
Rio embedded sustainability into the everyday language and practice of city planning, framing local action as essential to global environmental goals. The Local Agenda 21 model spread participatory environmental planning to thousands of municipalities worldwide.