Aqueous-core capsules with uniform polymeric shells and diameters ranging from 0.2 to 5 µm were prepared by polymerizing the interfaces of inverse emulsion microspheres. Free-radical polymerization was constrained to the interface of water-in-oil microspheres by the alternating copolymerization of hydrophobic maleate esters and hydrophilic polyhydroxy vinyl ethers, in a manner analogous to classical interfacial polycondensations. In these polymerizations, the kinetics, shell thickness, and release characteristics of the resulting aqueous-core capsules are set by the diffusion limited alternating reaction of the oil-soluble maleate esters and water-soluble vinyl ethers.