This paper was presented at the Tall Buildings and Urban Habitat Sixth World Congress – Cities in the Third Millennium, Melbourne, 2001. The Council on Tall Buildings and Urban Habitat (CTBUH) is an international organisation sponsored by architectural, engineering, planning, and construction professionals. The council aims to facilitate professional exchanges among those involved in all aspects of the planning, design, construction and operation of tall buildings. Of major concern is the role and impact of tall buildings on the urban environment.