Water is the most common and, judged from its numerous anomalous properties, the weirdest of all known liquids and the complexity of its pressure-temperature map is unsurpassed. A major obstacle on the way to a full understanding of water’s structure and dynamics is the hard-to-explore territory within this map, colloquially named the no man’s land. Many experiments suggest that just before stepping across its low-temperature border, amorphous ices undergo glass-to-liquid transitions while other interpretations emphasize the importance of underlying disordered (nano)crystalline states. Prospects for reconciling the conflicting views regarding the nature of water’s glass transitions are discussed.

• Received 5 May 2015

DOI:https://doi.org/10.1103/RevModPhys.88.011002