With the rising population in the city centers, smart cities experience a pressure to handle waste in a sustainable way and enhance resource efficiency and environmental quality. The chapter examines the application of circular nanotechnology in strategically designed waste management systems in smart cities to create cleaner, data-driven, and resource-recovering urban environments. Nano-enabled sensors and nanomaterials provide new solutions in real-time waste monitoring, separation, degradation, and recycling of complex waste products, e.g., plastics, e-waste, and organic matter. The chapter talks about nano-enabled biosensors used in monitoring at bin level, nanocatalysts used in waste-to-energy, and nanomembranes used in the treatment of leachate and the removal of pollutants. Connection to IoT systems and AI will make automation, predictive analysis, and decision-making more effective in urban waste authorities. Case studies have been used to emphasize implementation in pilot smart cities and how circular nanotechnology can help reduce landfill, provide a material recovery, and help achieve climate action objectives. The issues of scaling, cost-efficiency, and policy regulation are also discussed in the chapter. Circular nanotechnology is an interdisciplinary discussion that places it as a transformational enabler to construct cleaner, resilient, and smart cities in the future.