This paper builds an argument that is developed more fully in the book The Green City, Sustainable Homes, Sustainable Suburbs. It starts with a discussion of the meaning of 'sustainability' and the global ecological crisis our world confronts. The discussion then turns to the strategies cities need, and the barriers to innovative policies. Finally the paper shows that tactical solutions have already been demonstrated around the world. Architects and planners can play a major role in carrying forward the agenda of 'the green city'. Town planning will have to change; removing barriers to green policies and engaging in urban transport as well as land use planning. Above all, planning the green city demands institutional and not just policy change, and a more real multidisciplinary approach.