As contributor Jude Clemente points out, energy efficiency is an important aspect of any modern energy system. It is not, however, a panacea for solving all energy and power supply and demand challenges. Historical evidence points to the fact that energy efficiency at the micro-level doesn’t reduce overall energy demand on a macro-level. This can be seen in the oil market where, as prices rise and fall, in spite of efficiency gains in automotive technologies measured by miles-per-gallon, consumers adjust their buying habits accordingly e.g. buying more gas as prices fall and curtailing spending when the price of gas goes up. However, in the vehicle market, despite efficiency gains over the last three decades, Americans are driving more and consuming more oil than ever before. Clemente’s article explores energy efficiency in the United States across three domains: the macro-economy, the vehicle fleet, and the electricity sector.