Polymeric micelles are assemblies of synthetic polymers and have been studied and developed as drug carriers for targeting. Polymeric micelles are composed of the inner core and the outer shell, and typically form from AB-type block copolymers in which two polymer blocks are connected in a tandem form. Polyethyleneglycol (PEG) has been most commonly used as one polymer block composing the outer shell. This review describes the reasons that PEG is used for the outer shell of the polymeric micelle carrier systems. On the other hand, accelerated blood clearance (ABC) phenomenon is a well-known immunological response of PEG-coated liposomes. Since the ABC phenomenon greatly influences targeting functions of carrier systems, elaborative studies on polymeric micelles’ ABC phenomenon have been done, and revealed different behaviors of the polymeric micelle systems from those of PEG-coated liposomes. These studies indicate that polymeric micelle systems are highly feasible tools for contrast agent targeting as well as theranostics.