This book presents the 6G powered integration of Artificial Intelligence (AI) and Digital Twin (DT) technology for sustainable smart cities. In the context of smart cities, 6G, AI and DT hold enormous potential for transformation by boosting city infrastructure and planning, streamlining healthcare facilities, and improving transportation. 6G offers high speed and low latency seamless transfer of vast amounts of data which, when analysed with sophisticated AI models, enhance the decision-making capabilities for smart city infrastructure and urban planning. DT technology, through continuous monitoring and virtual modeling of urban ecosystems, enables predictive maintenance for energy distribution, water management and waste management in a smart city landscape for environmental sustainability. Driving Innovation through AI and Digital Twin for 6G Powered Sustainable Ultra Smart Cities covers the 6G technological innovations, trends and concerns, as well as practical challenges encountered in the implementation of AI and DT for transforming smart cities for a sustainable future.