 Phosphorous-based flame retardants have been used for decades as effective alternatives to traditional halogens in polymers and other materials. These flame retardants can be categorized into two main groups, those which enhance charring, condensed phase, and those which inhibit combustion, gas phase. The effectiveness of these flame retardants depends on their interactions with the polymeric material and any additives present. Understanding how these interactions affect the performance of the flame retardant is key to developing more efficient and targeted products. This article was authored by Bernhard Schartel.