The Sustainable Cities Program is an ambitious attempt to promote urban sustainability, recognizing the unique window of opportunity that comes with rapid urbanization. As mayors in developing countries seek to transform cities as inclusive and resilient hubs of growth, there is a growing demand for innovative tools and knowledge to help them make informed decisions. Initiatives such as the Compact of Mayors, C40 Large Cities Climate Leadership Group are already playing an important role in helping address this need; GEF is working with these initiatives to further strengthen the overall support for cities.