The Moskstraumen or Moskenstraumen is a system of tidal eddies and whirlpools, one of the strongest in the world, that forms at the Lofoten archipelago in Nordland county, Norway between the Norwegian Sea and the Vestfjorden. It is located between the Lofoten Point (Norwegian: Lofotodden) on the island of Moskenesøya (in Moskenes Municipality) and the island of Mosken (in Værøy Municipality). Moskstraumen is unusual in that it occurs in the open sea whereas most other whirlpools are observed in confined straits or rivers. It originates from a combination of several factors, the dominant being the strong semi-diurnal tides and peculiar shape of the seabed, with a shallow ridge between the Moskenesøya and Værøya islands which amplifies and whirls the tidal currents.

The Moskstraumen has been featured in many historical accounts, generally exaggerated. It is also popularly known as maelstrom – a Nordic word (malstrøm/malström) for a strong whirlpool which originates from the Dutch combination of malen (to grind) and stroom (stream). This term was introduced into the English language by Edgar Allan Poe in 1841, through his short story "A Descent into the Maelström". Poe provides an alternative name for the whirlpool with the line: "We Norwegians call it the Moskoestrom, from the island of Moskoe in the midway."