That water can exist in two distinct ＇glassy＇ forms-low- and high-density amorphous Ice-may provide the key to understanding some of the puzzling characteristics of cold and supercooled water, of which the glassy solids are more-viscous counterparts. Recent experimental and theoretical studies of both liquid and glassy water are now starting to offer the prospect of a coherent picture of the unusual properties of this ubiquitous substance.