By Dr Tony Tan Keng Yam - President of the Republic of Singapore

Singapore has come a long way in its journey towards sustainability. In the 1960s, Singapore was like any other developing country of that time – dirty and polluted, lacking proper sanitation and facing high unemployment.

By Joan Clos - Secretary-General of Habitat III and Executive Director of UN-Habitat

Habitat III, the Third International Conference on Housing and Sustainable Urban Development, offers the world an exceptional opportunity to rethink the sustainability of our urban model. It is largely recognized that cities have become the main driver of economic development.

By Margaret Chan - Director-General, World Health Organization

Health needs to be an integral part of Habitat III, the Third UN Conference on Housing and Sustainable Urban Development, and of its outcome.

By Charlie Hales - Mayor of Portland, Oregon, United States of America

One November afternoon, the Portland City Council chambers were filled with men and women in suits, serious and practical. Standing out in the crowd were two middle school girls, poised but nervous.

By Mauricio Rodas Espinel - Mayor of Quito, Sustainable City Envoy for ICLEI - Local Governments for Sustainability, including for Habitat III

Europe, Africa and Latin America now each have roughly half a billion people living in cities. In Asia, there are two billion city-dwellers. Very soon, two-thirds of the global population will be urban.

By Robert Doyle - Lord Mayor of Melbourne, Australia

Melbourne has just been named the World’s Most Liveable City for the sixth consecutive year. Naturally I am tremendously proud of that, but such an accolade cannot be achieved without a strong focus on sustainability.

By Federico Gutiérrez Zuluaga - Mayor of Medellin, Colombia

Remarkably, Medellin is now a global reference point for urban planning, efficient governance and social inclusion; moreover, the city has undergone a major transformation to get there.

By Dieter Salomon - Mayor of Freiburg, Germany

In recent decades there has been an unprecedented increase in the proportion and number of people living in urban environments. In 2014, 54 per cent of the world's people were urban dwellers, compared to 34 per cent in 1960.

By Luis Revilla Herrero - Mayor of La Paz, Bolivia

Latin American cities are going through accelerated urbanisation and reflect high levels of inequality. The continent is the world's most urbanised developing region, with eight out of ten people living in cities.

By Marcelo Mena - Vice-Minister of Environment, Chile

Since 2014, Chile’s Ministry of Environment has focused on three objectives: identifying and addressing the climate effects of air pollution; taking a leading role on addressing short-lived climate pollutants (SLCPs); and working to integrate these two concepts at both the local and global level.