This book explores the impact of population aging on energy use patterns in society from both a theoretical and an empirical angle, with a specific focus on Japan and Spain. Many developed countries are currently experiencing both population aging and population decline, while the demand for social services, such as health care and public transportation, is expected to increase. This book expands upon these well-known socioeconomic challenges and explores the less well-known and more complex relationship between population aging, time allocation to social practices, and energy resource consumption. In the face of energy supply scarcity and climate change concerns, the impact of population aging on energy consumption is of paramount importance. By focusing on the effects of changing time allocation patterns on social practices, the book shows that the impact of population aging on energy consumption will affect not just only affect the residential sector but also other socio-economic sectors of society. Using data from Japan and Spain – currently among the fastest- aging countries in the world – the volume shows that the challenges of an aging society are far more complex and worrying than previously anticipated. If an aging society is an inevitable future, we need to prepare for the challenges that lie ahead. Written by researchers in the fields of demography, economics, environmental engineering, geography, physics, and transportation engineering, this book will compel academics and policy makers to reflect on these problems and act. The Open Access version of this book, available at http://www.taylorfrancis.com, has been made available under a Creative Commons Attribution-No Derivatives 4.0 International (CC BY-ND) 4.0 license.