In the last past dozen years, polymersomes (Ps) have attracted tremendous attention as versatile carriers because of their colloidal stability, tunable membrane properties and ability in encapsulating or integrating a broad range of drugs and molecules. Relatively long blood circulation times of Ps can be accomplished when block copolymers with a poly(ethylene glycol) (PEG) are used for the formation of Ps. A number of Ps has been developed for new possibilities and applications in drug delivery, medical imaging, electronics and nanoreactors. In particular, Ps prepared by using biodegradable and/or stimuli-sensitive block copolymers that are responsive to various internal or external stimuli are of great interest for such applications. In this review, recent advances of Ps as drug delivery systems are discussed. Critical factors that influence the formation of Ps are also addressed. The review describes preparative methods and characterization techniques for Ps. Moreover, protein and cell interactions with Ps, in vivo circulation kinetics and biodistribution of Ps are addressed.