This book contains the proceedings of the 15th KES International Conference on Sustainability and Energy in Buildings 2023 (SEB2023) held in Bari, Italy, during September 18–20, 2023, organized by KES International. SEB23 invited contributions on a range of topics related to sustainable buildings and explored innovative themes regarding sustainable energy systems. The conference formed an exciting chance to present, interact, and learn about the latest research and practical developments on the subject. The conference attracted submissions from around the world. Submissions for the full-paper track were subjected to a blind peer-reviewed process. Only the best of these were selected for presentation at the conference and publication in these proceedings. It is intended that this book provides a useful and informative snapshot of recent research developments in the important and vibrant area of sustainability in energy and buildings.