This article reviews the applications of nanotechnology in the fields of medical and life sciences. Nanoparticles have shown promising applications from diagnosis to treatment of various types of diseases including cancer. In this review, we discuss the applications of nanostructured materials such as nanoparticles, quantum dots, nanorods, nanowires, and carbon nanotubes in diagnostics, biomarkers, cell labeling, contrast agents for biological imaging, antimicrobial agents, drug delivery systems, and anticancer nanodrugs for treatment of cancer and other infectious diseases. The adverse affects of nanoparticles on human skin from daily use in cosmetics and general toxicology of nanoscale materials are also reviewed.