Gahn is a Swedish family, one member of which was ennobled in 1809 with the name Gahn af Colquhoun. The family has claimed an unverified origin in a Scottish family Colquhoun, a claim which was confirmed 1781 in a letter by the Lord Lyon King of Arms, but on dubious grounds, as later research has shown. A claim that the Swedish noble family Canonhielm is a branch of this family has also been shown to lack genealogical substance.