The interest on poly(organophosphazenes) dates back to 1965, the official date of the synthesis of linear polydichlorophosphazene, and expanded rapidly to the synthesis and characterisation of poly(organophosphazenes), and their potential and practical use in different fields. Nowadays, phosphazene substrates occupy an important position in the panorama of inorganic-organic materials, somewhere at the borderline among the inorganic, organometallic and organic chemistry, and among polymeric, ceramic and metallic materials. Furthermore, theoretical aspects on their structures are still of importance in the scientific debate and their intriguing characteristics deeply investigated.