Over the past decade, RNA nanotechnology has witnessed significant advancements, with the synthesis of diverse RNA nanoparticles programmable in shape, size, and stoichiometry for broad nanobiotechnology applications. This progress is driven by breakthroughs in nucleotide chemical modifications that reduce RNA degradation, enhanced understanding of RNA’s high thermodynamic stability suitable for in vivo applications, and improved control over its immunogenic properties. Innovations in defining RNA’s complex 4D structure and dynamic intermolecular interactions, alongside reduced synthesis costs and demonstrated therapeutic safety and specificity, particularly in cancer treatment, further underscore its potential. This chapter will detail these advancements, illustrating RNA nanoparticles as programmable smart complexes and exploring future research directions in creating complex structures for applications ranging from tissue engineering to computer logic components, marking RNA nanotechnology as a transformative field in both biotechnology and medicine.