The concept of sustainable development rests upon three main principles: solidarity, precaution and participation. In 1992, the Rio Declaration stated the necessity of understanding economic development with social and environmental aspects integrated into it, and more than 180 countries, including Switzerland, signed a global action plan for sustainable development, known as Agenda 21. The Charter of European Cities and Towns Towards Sustainability (Aalborg Charter) was established two years later, and Lausanne agreed to it in 1998. Since 2000, Lausanne’s Agenda 21 has been organized around topical sections affecting all areas of public activity.