This article will discuss how my colleagues and I have promoted energy efficiency over the last 40 years. Our efforts have involved thousands of people from many different areas of expertise. The work has proceeded in several areas:• Investigating the science and engineering of energy end‐use,• Assessing the potential and theoretical opportunities for energy efficiency,• Developing analytic and economic models to quantify opportunities,• Researching and developing new equipment and processes to bring these opportunities to fruition,• Participating in the development of California and later federal standards for energy performance in buildings and appliances,• Ensuring that market incentives were aligned with policies, and• Designing clear and convincing graphics to convey opportunities and results to all stakeholders.