The sustainable development imperative has revived a forgotten, or discredited, idea: that planning ought to be done, or can be done, on a big scale. Up to the 1960s planning had a long, and reasonably creditable, history of visionary ideas. After that date, the public lost confidence in planners, and planners lost confidence in themselves. Subsequently, pragmatism has ruled. However, there is now a fascinating debate underway about the role of planning in promoting sustainable development, and-here we have the big idea-about which urban forms will most effectively deliver greater environmental protection. Viewed as a narrow environmental debate, the issue is profoundly important. But when the broader economic, social and cultural repercussions are taken into account, it soon becomes apparent that nothing less than the future of western lifestyles is at stake.