A veritable sea change in attitude about the performance of heritage buildings and systems has placed them prominently into the sustainability equation. Far from their maligned reputation as “energy hogs,” our historic buildings are increasingly recognized for their inherent energy efficiency—thermal mass, durability, indigenous materials, passive systems, integrated landscapes, embodied energy and regional design distinctions. The key lies in holistically identifying, then fine-tuning, existing elements within systems, buildings and communities that affect energy consumption, coupled with data collection of actual performance to prove out results. The authors will demonstrate through case studies a significant reduction in the cost and scope of interventions, along with greatly enhanced appreciation and operation of historic buildings, ultimately benefiting economy, environment and community.