The field of drug delivery has undergone a transformative paradigm shift with the advent of nanoscience and nanotechnology. This chapter explores the fundamentals of nano-based drug delivery systems, shedding insights into the innovative approaches and key principles that underpin their design and application in the realm of biomedicine. Beginning with a comprehensive overview of nanotechnology, this chapter delves into the unique properties of nanomaterials that make them ideal for drug theragnostics. Various forms of nanocarriers, including plasmonic nanoparticles, polymeric liposomes, micelles, vesicles, and dendrimers, are discussed, emphasizing their structures, fabrication methods, and the inherent advantages they offer in optimizing imaging, diagnostics, and drug delivery. The chapter also addresses the critical role of surface modifications and targeting strategies employed to enhance the specificity and efficacy of nano-based drug carriers. Ultimately, this chapter serves as a comprehensive guide for researchers and clinicians, illustrating the clinically approved nano-based formulations for clinical purposes, fostering the realization of more effective and targeted therapeutic interventions.