This article reviews the recent developments in the synthetic strategies to chemically modify several chain-growth polymers that were primarily developed in our laboratories, with a view to improve their flame retardance. In addition, it also incorporates the corresponding methodologies for the step-growth thermoplastics and thermoset materials. For chain-growth polymers, this involves primarily copolymerization reactions, under radical initiation, of acrylic or styrenic monomers with phosphorus-containing comonomers, or optionally, by post-modification reactions on preformed olefinic polymeric substrates with appropriate phosphorus-containing reagents. In the case of step-growth polymers, generally, an appropriate phosphorus-bearing moiety is employed, as one of the reactive components, during the step-growth synthetic process. The relative predominance of vapor- and condensed-phase mechanisms of flame retardance in the modified systems was evaluated through a combination of various analytical techniques. It was found that incorporation of phosphorus, through chemical modification reactions, on to the various thermoplastics resulted in substantial increases in the flame retardation. Furthermore, mechanistic aspects of flame retardation revealed both vapor-phase and condensed-phase elements depending on the chemical nature of the parent polymer in question and to a lesser extent on the chemical environment of the phosphorus-bearing moiety. Copyright © 2011 John Wiley & Sons, Ltd.