The basic compositions, manufacturing processes, and applications of diazo and vesicular microfilms are described. Both films are considered as variants of a photographic system based on the response of a diazonium salt to imaging actinic radiation. The two films are produced on a commodity basis and are generally the preferred duplicating films for COM (computer-output on microfilm), for source document material, and for an increasing number of micropublishing applications by virtue of their unique cost-effectiveness and simplicity of processing. Comparisons are made between the two films to provide a basis from which a film selection might be made for particular applications. (Abstractor's note: This is an extensive tutorial paper.)