Recently, medical applications of nanotechnology have received much attention. Among them, drug delivery systems (DDSs) are expected to be the leading technology in diagnostic and therapeutic medicine. An increasing number of DDSs have been approved for clinical use or are currently being studied in clinical trials. Polymeric micelles, self-assemblies of block copolymers, are one of the most refined and promising modalities of DDSs, since the critical parameters such as size, drug loading, and release can be controlled by engineering the constituent block copolymers. It has been demonstrated that polymeric micelles show unique disposition characteristics in the body suitable for drug targeting (e.g., prolonged blood circulation and significant tumor accumulation). Also, recent advances in polymer synthesis have allowed the development of polymeric micelles with integrated smart functions such as environmental sensitivity and targetability. Thus polymeric micelles might have great potential for nanotechnology-based DDSs for clinical use.