A series of polyanions and polycations have been synthesized from atactic, syndiotactic, and isotactic forms of poly(methyl methacrylate) and used to construct polyelectrolyte multilayers (PEMs). Polymer tacticity has been found to have a large influence on film growth but only a slight effect on H-2/N-2 permeation selectivities and no significant influence on CO2/N-2 permeation selectivities. The permeances of H-2, CO2, and N-2 across those PEMs exhibiting the highest H-2/N-2 selectivities were found to vary by as much as factors of 3, 6, and 5, respectively, depending on the tacticities employed. A simple model that accounts for the strong dependency of film growth on tacticity is presented.