In Norse mythology, Mjolnir is the hammer of Thor, the god of thunder. Distinctivly shaped, Mjolnir is depicted as one of the most fearsome weapons in Norse mythology in late Icelandic sources. There, it is used to slay any challengers. Though generally recognized and depicted as a hammer, Mjolnir is sometimes referred to as an axe or club. Legends surrounding Mjolnir's origins vary: some relate that the Svartálfar Sindri and Brokkr made it at the command of Loki.

Mjolnir simply means "crusher," referring to its pulverizing effect. It is related to words such as the Icelandic verbs mölva ("to crush") and mala ("to grind"), but similar words, all stemming from the Proto-Indo-European root melə can be found in almost all European languages, e.g. the Slavic melvo ("grain to be ground") and molotu ("hammer"), the Dutch meel ("meal"), the Russian Молоток (molotok - "hammer"), the Greek μύλος (mylos - "mill") and the Latin malleus ("hammer") as well as the Latin mola ("mill"). The English meal, mill and maul are direct relatives, while mallet, "malleable" and molar arrived via Latin. It has been suggested that although the name reflects Mjolnir's awesome powers it might also allude to Thor's agricultural nature, as he was primarily worshiped by farmers.

Many practitioners of Germanic Neopagan faiths wear Mjolnir pendants as a symbol of that faith worldwide.