As flammable polymeric materials become more ubiquitous in consumer goods, home furnishings, and transportation, there is a growing need for safe and effective flame retardant treatments. Recent studies suggest that certain flame retardant chemistries exhibit environmental and health problems, which has prompted the development of new flame retardant technologies. Layer-by-layer assembly has emerged as a promising technique for depositing environmentally-benign flame retardants on a variety of polymeric substrates. This technology has allowed the translation of common flame retardant mechanisms onto the surfaces of flammable polymers in the form of nanometer-scale coatings. Significant reductions in heat release rates and smoke release, as well as the ability to self-extinguish in open flame tests, have been observed on a variety of substrates. This review provides a comprehensive description of flame retardant multilayer nanocoatings on textiles, foams, and bulk polymers, as well as insight into the future direction of this growing field.