Brunost is a brown Norwegian whey cheese, also popular in Sweden, where it is called mesost. The Norwegian name brunost means 'brown cheese'. In North America it is referred to and sold as gjetost, which is an older spelling of geitost that is no longer frequently used elsewhere. The two most popular varieties in Norway are Gudbrandsdalsost, which means 'cheese from the Gudbrandsdal' (made from cow's milk), and the more traditional version geitost, which simply means 'goat cheese', and which is wholly or in part made from goat's milk. There are also regional varieties, which vary both in colour and taste, depending on how much caramel they contain. In Sweden, Fjällbrynt Mesost is produced by Milko in Östersund.

Geitost has a strong, sweet, yet somewhat sharp flavor with notes of caramel and goat's milk, while Gudbrandsdalsost is similar but more mellow in taste. The two varieties are often used as open sandwich toppings, on bread or malt loaf, or together with lefse. Brunost and lefse are used in some areas as a side dish to lutefisk.

Geitost is also used in game sauces, often together with juniper berries. It gives such sauces a more subtle, caramel taste.