**Prefaceto"EnergyEfficientCitiesofTodayandTomorrow"**

The world needs to undergo a rapid transformation to a sustainable low-carbon consumption system. With the ongoing urbanization and ever-growing harmful environmental impacts from urban areas, the focus of this required sustainability transformation is on cities. However, cities are centers of wealth creation and economic growth, also known as two of the main drivers of environmental degradation. Cities also provide their citizens with evermore diverse consumption opportunities, making the lifestyles of city dwellers more and more consumption-oriented. This inevitably leads to increased energy demands and emissions in cities due to needed infrastructure and real estate development, the increased energy demands of users, and the increased energy embodied in the goods and services consumed within cities. Concurrently, we are facing imminent pressure to significantly reduce our energy consumption and greenhouse gas emissions at all levels of society. This pressure urges cities to re-establish themselves as low-energy/low-carbon urban ecosystems, but the transformation is difficult and complex in many ways, and time is running out rapidly. A lively academic discourse on the issue has been ongoing for several years, but so far without widely accepted or unanimous solutions. This Special Issue, "Energy Efficient Cities of Today and Tomorrow", seeks to enhance this conversation and provide a more profound understanding of the future energy requirements of urban areas and low-energy and low-carbon cities. The nine published papers range from macro-level assessments of cities manifesting themselves as forerunners in their environmental work to micro-level studies of pro-environmental attitudes and their impacts on individual emissions, as well as impacts on the carbon footprint from sharing goods and services. They present potential solutions and introduce new discussion points to find potential pathways to a truly sustainable future.

> **Jukka Heinonen, Sanna Ala-Mantila, Ortzi Akizu-Gardoki** *Editors*
