The development of nanomaterials for biomedical applications over the last 20 years has shown great potential for altering the way that all facets of illness management are thought to be approached. Since nanomaterials may be customized to incorporate features for early diagnosis, medication delivery, therapy, treatment, and patient response monitoring, they are particularly appealing as a system. The realm of functionalized nanomaterials is characterized by its diversity and rapid evolution, with ongoing research endeavors focused on discovering novel functionalities and applications for nanoscale materials. Functionalized nanomaterials play a pivotal role in nanobiomedicines and diagnostic devices, contributing significantly to advancements in these fields. The use of functionalized nanomaterials varies from cancer therapy, drug delivery, cosmetics, and medical use to various other entities. Therefore, this chapter reviews the fundamentals of nanomaterials fictionalization, surface fictionalization, and different nanomaterials that are contributing to drug delivery and diagnostic devices.