Polymersomes are nanovesicles (“hollow sacks”) that are comprised entirely of FDA-approved biodegradable polymers that spontaneously self-assemble in water. Compared to other nanocarriers, polymersomes have several distinct advantages including larger loading capacities and superior formulation stabilities. As such, polymersomes are particularly useful for the stable encapsulation of both water-soluble and insoluble agents, in high concentration, without the need for chemical modification of their cargo. They have successfully been used to deliver a wide variety of agents, including small molecules, peptides, proteins, and nucleic acids for diagnostic and therapeutic applications. Further, polymersomes’ unique structural properties enable specific delivery to target sites without concomitant loss of their cargo due to premature breakdown after prolonged shelf-storage or in high shear flow, in vivo vascular environments.