The polydiacetylenes have received much attention in recent years because of their large non-resonant third-order nonlinear optical response and because of the flexibility they offer in designing tailored molecular structures for specific applications. However, the fabrication of these materials into device-quality thin films has proven to be difficult, largely because of their propensity for forming highly scattering polycrystalline solids (with the exception of the few soluble polydiacetylenes, such as 3- or 4-BCMU, which can be spin-coated by conventional techniques, albeit in the less-active yellow form of the polymer). We have addressed this problem by developing a family of polydiacetylene "alloys": polymers derived from mixtures of similar diacetylene monomers having identical positioning of the diacetylene unit within the hydrocarbon chain, but with different "head" groups that provide varying degrees of affinity to water. The rationale here has been to design mixtures that would form a uniform, quasi-amorphous monolayer on the water surface in Langmuir-Blodgett multilayer fabrication, and thus avoid the scattering losses associated with grain boundaries that form within the monolayer on the water surface. To date, multilayer films up to 0.4 um thick have been fabricated by this approach, and photolithographic techniques have been developed for patterning strips down to 4 um wide in the films, without converting the blue form of the polydiacetylene to the red form in the process. Moreover, high quality films of polydiacetylene have been deposited successfully onto curved surfaces, such as polycarbonate lens blanks, using these compositions.