An ice cap is a thick layer of ice and snow that covers large areas of land, usually covering a highland area. Ice caps are not constrained by topographical features, meaning they will lie over the top of mountains. By contrast, ice masses of similar size that are constrained by topographical features are known as ice fields. Ice caps are formed when snow is deposited during the cold season but doesn’t completely melt during the hot season. Over time, the snow builds up and becomes dense, well-bonded snow known as perennial firn. Finally, the air passages between snow particles close off and transform into ice.

Key features of an ice cap include:

• Size: An ice cap is a mass of ice that covers less than 50,000 km² of land area. Larger ice masses covering more than 50,000 km² are termed ice sheets.
• Shape: The shape of an ice cap is determined by the landscape it lies on, as melting patterns can vary with terrain. For example, the lower portions of an ice cap are forced to flow outwards under the weight of the entire ice cap and will follow the downward slopes of the land.
• Climate: An ice cap climate is a polar climate where no mean monthly temperature exceeds 0 °C (32 °F). The climate generally covers areas at high latitudes and polar regions (60–90° north and south latitude). Since the temperature never exceeds the melting point of ice, any snow or ice that accumulates remains there permanently, over time forming a large ice sheet.

Ice caps have been used as indicators of global warming, as increasing temperatures cause ice caps to melt and lose mass faster than they accumulate mass. Ice cap size can be monitored through different remote-sensing methods such as aircraft and satellite data.