A series of poly(N-alkyl-4-vinylpyridinium halide)s was prepared by reacting (sic) poly(4-vinylpyridine)s [M(v)BAR, 25 000 and 42 700] with a range of straight-chain alkyl halides. The smallest alkyl halide used was 1-bromooctane; the largest was 1-bromodocosane. The percentage of pyridine moieties quaternized was usually greater-than-or-equal-to 91%, though several polymers were prepared where the percentage was deliberately ca. 50%. Monolayers of the various products on water displayed good isotherms which included significant "solid" regions and collapse pressures greater-than-or-equal-to 26 mN/m. The monolayers could be transferred onto silicon wafers that had been treated to make them hydrophobic. The monolayers of polymers with side chains containing less-than-or-equal-to C-11 transferred well on the upstroke and not at all or only partially on the downstroke, though low-angle X-ray diffraction experiments indicated that the multilayers produced had Y-type structures. Monolayers of polymers with side chains containing greater-than-or-equal-to C-12 deposited well on both the upstrokes and downstrokes to give Y-type multilayers in which the side chains were interdigitated. Evidence for the latter was obtained by low-angle X-ray diffraction experiments and FTIR measurements. As judged by X-ray diffraction experiments, the best interdigitated structures were obtained when the side chains contained 18-, 20-, or 22-carbon atoms. Two of these displayed four Bragg peaks and one five. UV irradiation of Langmuir-Blodgett multilayers prepared from the polymer with 10-undecenyl side chains were rendered insoluble as a consequence of cross-linking.