Nanobiotechnology—at the interface of nanomaterials, biology, and medicine—has reshaped how we detect, visualize, and treat disease. Engineered nanosystems (lipid and polymeric nanoparticles, dendrimers, inorganic nanocrystals, and hybrid assemblies) provide high surface‐area scaffolds for biomolecule presentation, signal amplification, and precision delivery. In diagnostics, plasmonic and electronic nanosensors, quantum dots, and surface-enhanced Raman scattering (SERS) platforms enable ultrasensitive detection of nucleic acids, proteins, metabolites, and pathogens at the point of need. In therapeutics, ligand-decorated carriers, stimuli-responsive release chemistries, and immune‐cell–instructive nanomaterials enhance bioavailability, tune pharmacokinetics, and concentrate payloads at target sites—advancing oncology, infectious disease, gene therapy, and immunotherapy. Theranostic constructs integrate imaging and therapy for closed-loop guidance of interventions. Yet translation hinges on mastering nano–bio interface phenomena (protein corona, opsonization), scalable and reproducible manufacturing, rigorous safety evaluation, and equitable access. This paper surveys platform designs and applications across diagnostics and targeted therapeutics, distills design principles for clinical translation, and outlines regulatory, ethical, and manufacturing considerations that will govern impact in the coming decade.