In Norse mythology, Njörðr (Old Norse: Njǫrðr) is a god among of the Vanir. He is the father of the deities Freyr and Freyja by his unnamed sister, and had a failed marriage with the goddess Skaði, lives in Nóatún and is associated with the sea, seafaring, wind, fishing, wealth, and crop fertility.

Njörðr is attested in the Poetic Edda, compiled in the 13th century from earlier traditional sources, the Prose Edda, written in the 13th century by Snorri Sturluson, in euhemerized form as a beloved mythological early king of Sweden in Heimskringla, also written by Snorri Sturluson in the 13th century, as one of three gods invoked in the 14th century Hauksbók ring oath, and in numerous Scandinavian place names. Veneration of Njörðr survived into the 18th or 19th century Norwegian folk practice, where the god is recorded as Njor and thanked for a bountiful catch of fish.

Njörðr has been the subject of an amount of scholarly discourse and theory, often connecting him with the figure of the much earlier attested Germanic goddess Nerthus, the hero Hadingus, and theorizing on his formerly more prominent place in Norse paganism due to the appearance of his name in numerous place names. Njörðr is sometimes modernly anglicized as Njord, Njoerd, or Njorth.

The name Njörðr corresponds to that of the older Germanic fertility goddess Nerthus (early 1st c. CE). Both derive from the Proto-Germanic theonym *Nerþuz.

The original meaning of the name is contested, but it may be related to the Irish word nert which means "force" and "power". It has been suggested that the change of sex from the female Nerthus to the male Njörðr is due to the fact that feminine nouns with u-stems disappeared early in Germanic language while the masculine nouns with u-stems prevailed. However, other scholars hold the change to be based not on grammatical gender but on the evolution of religious beliefs; that *Nerþuz and Njörðr appear as different genders because they are to be considered separate beings. The name Njörðr may be related to the name of the Norse goddess Njörun.

Njörðr's name appears in various place names in Scandinavia, such as Nærdhæwi (now Nalavi, Närke), Njærdhavi (now Mjärdevi, Linköping; both using the religious term vé), Nærdhælunda (now Närlunda, Helsingborg), Nierdhatunum (now Närtuna, Uppland) in Sweden, Njarðvík in southwest Iceland, Njarðarlög and Njarðey (now Nærøya) in Norway. Njörðr's name appears in a word for sponge; Njarðarvöttr (Old Norse: Njarðarvǫttr, "Njörðr's glove"). Additionally, in Old Icelandic translations of Classical mythology the Roman god Saturn's name is glossed as "Njörðr".

Njörðr is described as a future survivor of Ragnarök in stanza 39 of the poem Vafþrúðnismál. In the poem, the god Odin, disguised as "Gagnráðr" faces off with the wise jötunn Vafþrúðnir in a battle of wits. While Odin states that Vafþrúðnir knows all the fates of the gods, Odin asks Vafþrúðnir "from where Njörðr came to the sons of the Æsir", that Njörðr rules over quite a lot of temples and hörgrs (a type of Germanic altar), and further adds that Njörðr was not raised among the Æsir. In response, Vafþrúðnir says:

In Vanaheim the wise Powers made him
and gave him as hostage to the gods;
at the doom of men he will come back
home among the wise Vanir.