The transition to a circular economy demands not only sustainable technologies but also transparent and traceable systems to monitor material flows, reduce waste, and ensure accountability. This chapter explores the synergistic integration of blockchain technology and nanotechnology to enhance transparency, traceability, and efficiency within circular economy frameworks. Blockchain, with its immutable, decentralized ledger, can securely record lifecycle data of materials and products, while nanotechnology enables advanced tracking through nanosensors, nano-barcodes, and smart materials embedded at the source. Together, these technologies offer real-time insights into material provenance, usage, recycling status, and environmental impact. The chapter discusses real-world applications in sectors such as e-waste management, pharmaceuticals, food packaging, and sustainable manufacturing. Key enablers like smart contracts, digital twins, and IoT-nano convergence are examined. Furthermore, it addresses the challenges of scalability, data privacy, energy consumption, and regulatory gaps. By presenting conceptual models and pilot implementations, this chapter underscores the potential of blockchain–nano convergence in building trustworthy, closed-loop systems that align with the goals of sustainable development and circularity.