Circular nanotechnology is an innovative way of addressing world sustainability problems by integrating nanomaterials and nano-processes into the circular economy system. This chapter discusses how circular nanotechnology has the potential to greatly contribute toward the achievement of the United Nations Sustainable Development Goals (SDGs), particularly in sustainable agriculture, clean water, accessible energy, sustainable consumption and production, and climate action. With accelerating global resource depletion and environmental degradation, nanoscale innovation offers promising pathways toward enhancing resource efficiency, minimizing waste, and enabling sustainable development. Fundamental concepts of circular nanotechnology, paradigm transition from linear to circular models, and alignment with Sustainable Development Goals are subjected to critical analysis. It selects applications such as nano-fertilizers for agricultural output (SDG 2), nano-enhanced water treatment technologies (SDG 6), nanomaterials for renewable energy technologies (SDG 7), environmentally friendly nanocomposites for sustainable production (SDG 12), and carbon capture technologies to combat climate change (SDG 13). Actual case studies provide the basis for conceptual analysis. In addition to illustrating the potential of nanotechnological innovation in closing material loops and making the world more resilient, the chapter also assesses associated risks like nanotoxicity and regulatory challenges. In illustrating real-world applications and current trends, it focuses on the central position of circular nanotechnology in leading a sustainable future and suggests increased research, international collaboration, and innovation policy.