The research focussed on how urban greyfields, especially abandoned big box retail, can be redeveloped into mixed-use walkable live/work neighbourhoods for an energy-efficient future. The history of shopping centre and big box retail and the mixed-use residential redevelopment of such sites using the new LEED Neighbourhood Development rating system were studied. Four principle concepts were found and used to guide the design projects. They were sustainable urbanism planning versus Modernist auto-dependency; mixed-use planning; walkable neighbourhood concepts; and live/work units. These help create local employment in transit-based neighbourhoods having nearby services and amenities to reduce commuting and auto-dependency. The design project on a 25-acre Toronto greyfield includes Continuous Productive Urban Landscapes for food production and a trail system promoting walking, cycling and greater contact with nature. Greyfield sites used for sustainable communities help offset valuable farmland losses and offer useful urban intensification possibilities for a looming energy crisis.