Keeping sustainability in mind, polymer composites are usually fabricated with biobased materials instead of synthetics. However, these “biocomposites” often lack the required strength and are extremely susceptible to fire. This necessitates the application of fire-retardant treatment, which could render the composite fire resistant. This chapter gives an overview of the types of fire retardants that are generally applied, and a review of studies done to impart fire retardancy in composites. Several instruments and standards used for determining fire behaviors of composites are also described in detail. Biochar (especially made at high pyrolysis temperatures) is very resistant to ignition and thermally stable, owing to its extensive network of cross-linking between adjacent aromatic carbon sheets. Its inclusion in polymeric composites is advantageous for both fire and mechanical properties. The inherent fire-resistant and char-forming ability of wool (a natural protein fiber) has been exploited to develop composites that exhibit the highest degree of flame resistance (V0 rating in UL94 tests). Finally, wheat gluten, a by-product of the cereal industry, has shown potential regarding fire retardancy and thermal stability. Gluten's flame-resistant properties can be made even more potent by applying other additives (e.g., silica).