Abstract Malaysian architect Dr. Ken Yeang is an architect-planner and is frequently described as one of the foremost eco-designers, theoreticians, and thinkers in the field of green design. He has been described as one of the world's leading advocates in ecological and passive low-energy design. He has designed over one hundred projects, and his theory of “bio-climatic” towers has had an impact around the world, fusing high-tech with organic principles. He was born in Penang, Malaysia, in 1948, and was educated in Penang, the United States, and at the Architectural Association in London. He received his doctorate in Architecture from Cambridge University in 1974. He is the author of a number of books on the topic of ecological planning and high-rise design (e.g., The Skyscraper: Bio-climatically Considered, 1996; Eco-Masterplanning, 2009). According to Yeang, the “bioclimatic” high-rise tower is a low-energy tower that is based on bioclimatic design principles and designed as a vertical urban design typology crossed by air and light wells and protected by sun shading devices. Bio-climatic in architecture means responding to the climate with minimal reliance on fossil-fuel energy for achieving comfort. Ken Yeang's definition of bio-climatic is based on the following concepts: The integration of the grey (engineering), blue (water), red (human), and green (landscape) infrastructures in projects of all scales; the bio-integration of the building as an artificial element into the biosphere; the eco-mimesis, repeating nature's patterns such as solar energy and waste equals food; the re-linking of ecosystems by bridging the existing natural areas; and, finally, the monitoring for rectifying and improving the existing built environment. His single-minded pursuit of eco-design through his own architectural practice and writing for over 35 years has influenced countless architects around the world. Major works by Ken Yeang include:•The IBM Malaysia Tower in Kuala Lumpur (1989–1992)•The National Library Building in Singapore (2000–2005) The National Library is the first building in Singapore to obtain the Green Mark Platinum award. It incorporates many passive and active design strategies, e.g., a large naturally-ventilated and lit atrium space; the use of external sun-shading louvers; and integrated greenery for thermal benefits. The total embodiment of the building (being its first costs) was calculated to be 17GJ/m2, an impressive result achieved through carbon footprint considerations in the selection of all building materials. The author met with Ken Yeang at the SASBE Conference in Delft, in June 2009, to discuss the future of sustainable urbanism and why our cities need to change. Here are excerpts from their conversation.