This article describes a joint urban design study by the Berkeley Environmental Stimulation Laboratory and the Centre for Landscape Research at the University of Toronto. The study analyzed the effect of future development in Toronto's Central Area on streetlevel conditions of sun, wind, and thermal comfort. The study originated in response to public concern about the quality of the downtown environment and to implementation measures adopted by the Toronto city council in May 1993. The research presented in this article examines the shadowing produced by downtown buildings and recommends procedures and standards for preserving sunlight on Toronto's downtown sidewalks and open spaces. Second, this study considers the effects of buildings on wind conditions at street level. Third, the study evaluates the combined effects of sun and wind conditions on pedestrian comfort. Rather than focusing on just the effects of individual buildings, this research evaluates the cumulative effects of area-wide development.