HDPE and LDPE composites are considered in various applications in everyday life. The need for a sustainable future suggests a low environmental impact of the composites in use throughout their life cycle. In this view, the reduction in carbon dioxide emissions can be approached by exploiting biocomposites and bionanocomposites. Consequently, natural fibers play a key role in such a product design. Current standards in critical sectors such as construction and transportation require, among others, high levels of fire resistance. Therefore, polyethylene biocomposites should also successfully meet the relevant stringent criteria. In this book chapter, several strategies which are advancing the flammability performance of the HDPE and LDPE biocomposites and bionanocomposites are discussed.