This document discusses nanoparticles as subnanosized colloidal drug delivery systems ranging from 10-1000 nm in diameter. It defines nanoparticles and describes their basic concept of selectively delivering drugs to target tissues while restricting access to non-target tissues. The document outlines ideal characteristics of nanoparticles and various methods for their preparation, characterization, and evaluation. It provides examples of nanoparticle applications such as cancer therapy, intracellular targeting, vaccines, DNA delivery, and ocular delivery. The document concludes by listing references for further information on nanoparticles.