Pure and doped niobium oxide (Nb 2 O 5) layers are electrochromic (EC) materials which change their color by insertion of Li + ions from transparent to brown, grey or blue depending on the crystallinity of the layer. EC devices with the configuration K glass/EC layer/composite electrolyte/ion storage (IS) layer/K glass, were produced using different Nb 2 O 5 EC layers, a (CeO 2) x (TiO 2) 1Àx (x 0.45) IS layer and an inorganic organic composite electrolyte to which a small amount of water (up to 3 wt.%) was added. The grey coloring all solid state sol gel devices fabricated with Nb 2 O 5 : Mo coatings show a high reversible coloration (DOD 0.3) and a long term stability of more than 55 000 switching cycles. Large area EC devices (30 Â 40 cm) show a transmittance change between 60% and 25% at 550 nm after galvanostatic coloration and bleaching for 3 min and a coloration efficiency of 27 cm 2 /C. The results obtained with blue and brown coloring Nb 2 O 5 EC layers and a comparison with blue coloring WO 3 layers are also presented.