All available data on bathymetry, temperature, salinity and currents up until and including 1975 are used in describing the seasonal changes and dynamics of tee hydrography of Disko Bugt, the Vaigat and adjacent glacier and non glacier fjords. From a winter situation with well mixed ÷1.75°C cold water in the upper c. 100 m steep halo- and thermoclines develop during the summer between freshened and heated surface water leaving Disko Bugt and deeper more saline water entering from the West Greenland Current. Huge ice bergs have a decisive cooling effect upon the upper 150-200 m affecting the outflowing current as well as the inflowing water which is responsible for the high bottom temperatures and salinities (up to 3.5°C and 34-34.5‰ at 400-500 m) found the year round, and which contributes to raising the temperature in the upper 200 m in the summer, especially in the southern and eastern part of the bay and even into the Vaigat. Surface temperatures reach 12°C in the offshore waters of the bay where salinities may drop to 30‰ and inshore in the more diluted waters of Disko Fjord temperatures may even reach 14°C, whereas in the glacier fjords, where surface salinities come close to zero, 4°C is the highest temperature recorded and subzero temperatures are found even in July. An extensive upwelling of W Greenland water occurs in the northern part of the bay during the summer and fall and similar phenomena occur in Disko Fjord, driven by winds and apparently linked to tidal rhythms. Although TS diagrams show that deep Disko Bugt water and Baffin Bay water is of common origin, no water seems to enter Disko Bugt from Baffin Bay or from the Baffin Current.