Polymersomes are self-assembled nano-vesicles composed of amphiphilic block copolymers. These building blocks can be selected from a large number of hydrophilic and hydrophobic polymers in order to achieve required properties of the final system, such as biodegradability, sustainable and multiple stimuli-response drug release, long blood circulation, and low toxicity. Moreover, the surface of polymersomes can be functionalized to induce targeting character. Polymersomes are able to encapsulate a broad range of hydrophilic or/and hydrophobic molecules either in the aqueous core or membrane bilayer, respectively. In addition, colloidal stability and low membrane fluidity make polymersomes attractive nano-sized drug carriers. The review describes polymersomes compositions, their applications in pharmaceutical delivery, and preparation methods.