Kolsås (Norwegian pronunciation: [ˈkôɫsoːs]), sometimes called Kolsaas, is a hill in the municipality of Bærum, Norway.

Its two peaks consist of hard rhomb porphyric lava covering softer rocks, forming steep cliffs to the east, south and west.

The parish and municipality of Bærum (Old Norse Bergheimr) is probably named after this prominent mountain.

Today it is the largest rock climbing area in the Oslo region.

The military base Kolsås leir, partly located inside the mountain, was home of NATO's Allied Forces Northern Europe (AFNORTH) until 1994.