This chapter discusses key issues related to the flame retardancy of textile materials using nanoparticles. Nanoparticles are considered regarding types, properties, and flame retardancy mechanisms. They are solid particles having sizes below 100 nm. Because of their higher surface areas, better chemical reactivity, magnetic, photoconductive abilities, and thermal stability, they are valuable materials for the functionalization of textiles. Nanoparticles that are used for improved flame retardancy and thermal stability of textile materials are discussed including metal-based, carbon-based, silica-based and organic nanoparticles. Moreover, mechanisms of combustion and flame retardancy of textiles are discussed together with the chemical and physical actions that nanoparticles exhibit in case of high heat and/or an ignition source. Nanoparticle application methods to textile materials to confer flame retardancy are given, and relevant to the properties of nanoparticles. The focus of the recent interesting research on flame retardancy of textiles by nanoparticles is discussed. Limitations of the use of nanoparticles in terms of the flame retardancy properties achieved are emphasized. Finally, future aspects for nanoparticle flame retardancy systems are highlighted.