This paper summarizes the principle of integrative design. Integrative design rigorously applies orthodox engineering principles, but achieves radically more energy- and resource-efficient results by asking different questions that change the design logic. Examples described in this paper for buildings, industry, and vehicles show that optimizing whole systems for multiple benefits, not disjunct components for single benefits, often makes gains in end-use efficiency much bigger and cheaper than conventionally supposed. Indeed, integrative design can often yield expanding rather than the normal diminishing returns to investments in energy efficiency, making very large (even order-of-magnitude) energy savings cost less than small or no savings.