The expanding scope of polyphosphazenes in materials science is described. This expansion involves new methods of synthesis that provide access to novel polymer architectures, and materials with useful combinations of properties that include superhydrophobic surfaces, biomedical materials, responsive membranes, photonic materials, battery electrolytes, fuel cell membranes, fire-resistant polymers, and new systems that generate micelles, stars, and dendrimers. (C) 2007 Elsevier Ltd. All rights reserved.