‘Glacier ice: discovery and understanding’ considers how and why glaciers are formed and the history of the study of glaciers, which has enhanced our knowledge. Glacier ice will form wherever the combined effects of precipitation (specifically snow), low temperatures, and topography create the optimum conditions. These optimum conditions are met in regions of high altitude and high latitude, but can be met at high altitudes in equatorial regions and lower altitudes towards the poles. Other conditions must also be satisfied: aspect, relief, and the distance from the nearest moisture source. The balance and equilibrium of glaciers is also explained along with their key features and how they act as archives of climate change.