The term “Green City” has many different meanings to different people. There is no universal solution that can be applied to every city. Adaptable, responsive, and innovative solutions that differ from one place to another enable Green Cities to emerge in various forms and enable us to recognize the variation and dynamism of cities. This tool kit is a reference for Asian Development Bank staff, consultants, and city leaders that introduces key concepts of Green City development and identifies crosscutting issues that help in designing urban programs to support city development in a green and sustainable manner.