This book explores how modern cities are transforming through smart technologies and circular economy principles. The opening chapters introduce the concept of the smart city, explaining digital infrastructure, data-driven decision making, and connected urban systems in clear, accessible language. The middle sections examine sustainable urban planning, focusing on energy efficiency, waste reduction, resource reuse, and innovative mobility solutions. Later chapters highlight real-world case studies, showing how cities around the world apply circular economy models to improve economic growth, environmental protection, and quality of life. The final sections look ahead, discussing policy, governance, and the role of citizens in shaping sustainable cities. By combining urban innovation, sustainability, smart technologies, and circular economies, this book offers a practical and forward-looking guide for researchers, students, planners, and anyone interested in the future of cities.