Grottasǫngr (or Gróttasǫngr; Old Norse: 'The Mill's Songs', or 'Song of Grótti') is an Old Norse poem, sometimes counted among the poems of the Poetic Edda as it appears in manuscripts that are later than the Codex Regius. The tradition is also preserved in one of the manuscripts of Snorri Sturluson's Prose Edda along with some explanation of its context.

The myth has also survived independently in modified forms in northern European folklore. Gróttasǫngr had social and political impact in Sweden during the 20th century as it was modernized in the form of Den nya Grottesången by Viktor Rydberg, which described conditions in factories using the mill of Grottasǫngr as a literary backdrop.

Though not originally included in the Codex Regius, Gróttasǫngr is included in many later editions of the Poetic Edda. Gróttasǫngr is the work song of two young slave girls bought in Sweden by the Danish King Frodi (cf. Fróði in the Prose Edda). The girls are brought to a magic grindstone to grind out wealth for the king and sing for his household.

The girls ask for rest from the grinding but are commanded to continue. Undaunted in their benevolence, the girls proceed to grind and sing, wishing wealth and happiness for the King. The King, however, is still not pleased and continues to order the girls to grind without interruption.

King Frodi is ignorant of their lineage and the girls reveal that they are descended from mountain-risar. The girls recount their past deeds, including moving a flat-topped mountain and revealing that they had actually created the grinding stone they are now chained to. They tell him that they had advanced against an army in Sweden and fought "bearlike warriors", had "broken shields", supported troops, and overthrown one prince while supporting another. They recount that they had become well known warriors.

The girls then reflect that they have now become cold and dirty slaves, relentlessly worked, and living a life of dull grinding. The girls sing that they are tired, and call to King Frodi to wake up so that he may hear them. They announce that an army is approaching, that Frodi will lose the wealth they've ground for him, that he will also lose the magic grindstone, and that the army will burn the settlement and overthrow Frodi's throne in Lejre. They are grinding this army into existence via the magic stone. They then comment that they are "not yet warmed by the blood of slaughtered men".

The girls continue to grind even harder and the shafts of the mill-frame snap. They then sing a prophecy of vengeance mentioning Hrólfr Kraki, Yrsa, Fróði and Halfdan:

Mölum enn framar.
Mun Yrsu sonr,
niðr Halfdanar,
hefna Fróða;
sá mun hennar
heitinn verða
burr ok bróðir,
vitum báðar þat.