Fossum Idrettsforening is a Norwegian sports club from , Grini, Østerås and Eiksmarka in Bærum. It has sections for cross-country skiing, biathlon, ski jumping, alpine skiing, Nordic combined, orienteering, and football, and was founded on 7 December 1918. It formerly had an athletics section. The cross-country skiing section has prominent members like Tore Bjonviken and Simen Østensen.