Block copolymer vesicles can be prepared in solution from a variety of different amphiphilic systems. Polystyrene-block-poly(acrylic acid), polystyrene-block-poly(ethylene oxide), and many other block copolymer systems can produce vesicles of a wide range of sizes; those in the range of 100-1000 nm have been explored extensively. Different factors, such as the absolute and relative block lengths, the presence of additives (ions, homopolymers, and surfactants), the water content in the solvent mixture, the nature and composition of the solvent, the temperature, and the polydispersity of the hydrophilic block, provide control over the types of vesicles produced. Their high stability, resistance to many external stimuli, and ability to package both hydrophilic and hydrophobic compounds make them excellent candidates for use in the medical, pharmaceutical, and environmental fields. (C) 2004 Wiley Periodicals. Inc.