The Königssee is a lake in the extreme southeast Berchtesgadener Land district of the German state of Bavaria, near the border with Austria. Most of the lake is within the Berchtesgaden National Park.

Lying within the Berchtesgaden Alps in the municipality of Schönau am Königsee, just south of Berchtesgaden and the Austrian city of Salzburg, the Königssee is Germany's third deepest lake. Located at a Jurassic rift it was formed by glaciers during the last ice age. It stretches about 7.7 km (4.8 mi) in the north-south direction and is about 1.7 km (1.1 mi) across at its widest point. Except at its outlet, the Königsseer Ache at the village of Königssee, the lake similar to a fjord is surrounded by steeply rising flanks of mountains up to 2700 m (8900 ft), including the Watzmann massif in the west.

The literal translation appears to be "King's Lake"; however while German: König does indeed mean "king", there had been no Bavarian kings since the days of Louis the German until Elector Maximilian I Joseph assumed the royal title in 1806. Therefore the name more probably stems from the first name Kuno of local nobles, who appear in several historical sources referring to the donation of the Berchtesgaden Provostry in the 12th century; the lake was formerly called Kunigsee.