The Aletsch Glacier or Great Aletsch Glacier (Grosser Aletschgletscher) is the largest glacier in the Alps. It has a length of about 23km (2014), has about a volume of 15.4km3 (2011), and covers about 81.7km2 (2011) in the eastern Bernese Alps in the Swiss canton of Valais. The Aletsch Glacier is composed of four smaller glaciers converging at Concordia, where its thickness was measured by the ETH to be still near 1km. It then continues towards the Rhône valley before giving birth to the Massa.
The whole area, including other glaciers is part of the Jungfrau-Aletsch Protected Area, which was declared a UNESCO World Heritage Site in 2001.