Abstract <p>Early flame-retardants contained halogens, and while they were resistant to burning, the deadly organic or hydrogen halides produced during combustion were hazardous. Phosphorus–nitrogen-containing compounds are currently recognized as one of the most promising halogen-free flame-retardants due to their diversified structural makeup and good flame retardancy. The main focus of this review is on the recent developments in the synthesis of polycyclotriphosphazenes, ammonium polyphosphate, and melamine cyanurate, surface modifications, their importance and flame-retardant efficiency, cooperative actions and their properties, and their relevance for various polymers and fabrics. This review goes further into the reported literature, which frequently explains how phosphorus interacts cooperative with other environmentally promising flame-retardant components such as nitrogen, silicon, sulfur, and boron to increase FR efficiency. Finally, current barriers and future potential are discussed by examining the inherent weaknesses of P-N-based flame-retardants and the ever-increasing demand for flame-retardant materials.</p> Graphical abstract <p></p>