Kangerdlugssuaq Glacier, Tidewater outlet glacier in Sermersooq, Greenland.

Kangerdlugssuaq Glacier is the largest glacier on the southeast coast of the Greenland ice sheet, ending in a calving front about 1 km high that reaches the sea at the head of Kangerlussuaq Fjord, East Greenland's second-largest fjord. It is roughly 3 km thick and flows up to 14 km per year, among the fastest glaciers on Earth.

The glacier was discovered in 1930 and has been observed since 1932, when its floating ice tongue collapsed and it retreated 9 km, the largest retreat on record. It stayed fairly stable for decades, then retreated 5 km between April 2004 and April 2005, advanced about 200 m per year from 2008 to 2016, and retreated roughly 5 km in 2016–2018, reaching a position further inland than at any time in the previous 80 years before advancing again in the winter of 2018–2019.

The glacier's name comes from Greenlandic Kangerlussuaq, meaning "large fjord", after the Kangersertuaq fjord it drains into; the old spelling Kangerdlugssuaq is still used in English. It lies in Kong Christian IX Land in the Ammassalik district, Sermersooq municipality, East Greenland. Its ice has been observed since 1932, and it is one of several Greenlandic tidewater glaciers where glacier earthquakes have been recorded.

The glacier can be viewed from the water or from hiking trails along the coast, as the ice itself is too dangerous to approach closely on foot. Most visitors observe it from boats or guided excursions that offer safe vantage points.

The glacier's bed deepens inland and lies below sea level, a retrograde slope that makes it susceptible to Marine Ice Sheet Instability. Its floating tongue collapsed in 1932–1933, causing a 9 km retreat, larger than any recent event. It also ranks among the fastest-flowing glaciers on Earth, reaching up to 14 km per year, or 1.6 metres per hour, in 2005.