The solar envelope, first conceived and tested by the author working with architecture faculty and students at the University of Southern California (USC), regulates development within imaginary boundaries derived from the sun's relative motion. Buildings within this container will not overshadow their surroundings during critical periods of solar access for passive and low-energy architecture. If generally applied as an instrument of zoning, the solar envelope will not only provide for sustainable growth but will open new aesthetic possibilities for architecture and urban design. (C) 2003 Elsevier Science B.V. All rights reserved.