Mjölnir is the hammer of the thunder god Thor in Norse mythology, used both as a devastating weapon and as a divine instrument to provide blessings. The hammer is attested in numerous sources, including the 11th century runic Kvinneby amulet, the Poetic Edda, a collection of eddic poetry compiled in the 13th century, and the Prose Edda, a collection of prose and poetry compiled in the 13th century. The hammer was commonly worn as a pendant during the Viking Age in the Scandinavian cultural sphere, and Thor and his hammer occur depicted on a variety of objects from the archaeological record. Today the symbol appears in a wide variety of media and is again worn as a pendant by various groups, including adherents of modern Heathenry.

A hammer is a tool, most often a hand tool, consisting of a weighted "head" fixed to a long handle that is swung to deliver an impact to a small area of an object. This can be, for example, to drive nails into wood, to shape metal, or to crush rock. Hammers are used for a wide range of driving, shaping, breaking and non-destructive striking applications. Traditional disciplines include carpentry, blacksmithing, warfare, and percussive musicianship.