This article presents a critical assessment of research and practices that emerged over last 40 years that may be brought under the umbrella of “energy efficiency,” spanning different aggregations and domains – from individual producing and consuming agents to economy-wide effects, the role of innovation, and the influence of policy. It highlights advances in understanding the benefits of energy efficiency innovation, improvements in economic and measurement methods and tools, and progress in bending downward the energy use per unit economic output curve, which has taken over a century. We focus on how well deliberate policy actions have influenced energy users in the uptake of energy efficiency.  We also note how policies pursued thus far have put less attention on social welfare, inequity issues, and need to better account for complex dynamics associated with how micro actions affect macro outcomes, and to include a richer interdisciplinary approach.