In last few years, a rapid advancement in nanotechnology have provided many applications in the health sector and have great potential to solve the day-to-day problems faced during the treatment of various chronic diseases. One of the most important applications is the use of nanocarriers (NCs) for efficient and targeted drug delivery. Now a days, NCs such as organic, inorganic and hybrid NCs are of great interest owing to their wide application as drug delivery systems (DDSs). These NCs have a great deal of potential to minimize the drawbacks of present pharmacotherapeutics by improving therapeutic efficacy and biomolecular interactions, thereby lowering the side effects of various drugs. These systems often exhibit excellent stability, effective drug encapsulation and drug preservation against degradation. NCs are considered an alternative to drug diffusion into cells and can also be used as a diagnostic tool for various diseases. This chapter provides an overview of the functionalization of NCs by different classes of DDSs for diagnosing and treating human diseases.