Mer de Glace Glacier (MDG) is located in the Mont-Blanc valley (France), between 1500 and 3600 m altitude. The glacier is the larger glacier in France and one of the glaciers with longest records of glacier mass balance worldwide. Data series are continuous and cover few decades.This site is also characterized by the complete glaciological parameters performed annually to complete annual and seasonal mass balance: ice velocity, ice thickness variation, snout position.In addition, meteorological observations complete the data base. MDG is a part of the French Glacier Observatory GLACIOCLIM/CRYOBS-CLIM.