A housecarl (Old Norse: húskarl; Old English: huscarl) was a non-servile manservant or household bodyguard in medieval Northern Europe.

The institution originated amongst the Norsemen of Scandinavia, and was brought to Anglo-Saxon England by the Danish conquest in the 11th century. They were well-trained, and paid as full-time soldiers. In England, the royal housecarls had a number of roles, both military and administrative, and they fought under Harold Godwinson at the Battle of Hastings.

Housecarl is a calque of the original Old Norse term, húskarl, which literally means "house man". Karl is cognate to the Old English churl, or ceorl, meaning a man, or a non-servile peasant. The Anglo-Saxon Chronicle uses hiredmenn as a term for all paid warriors and thus is applied to housecarl, but it also refers to butsecarls and lithsmen. It is not clear whether these were types of housecarl or different altogether.

Originally, the Old Norse word húskarl (plural: húskarlar) (spelled huskarl, pl. huskarlar in Swedish) had a general sense of "manservant", as opposed to the húsbóndi, the "master of the house". In that sense, the word had several synonyms: griðmenn ("home-men") in Norway and Iceland, innæsmæn ("inside-men") in Denmark. Housecarls were free men, not to be confused with thralls (slaves or serfs); to this effect, the Icelandic laws also call them einhleypingar ("lone-runners") and lausamenn ("men not tied"). Both terms emphasise that they were voluntarily in service of another, as opposed to thralls.

With time, the term "housecarls" (húskarlar) came to acquire a specific sense of "retainers", in the service of a lord, in his hirð, lid or drótt (all meaning "bodyguard", "troop of retainers"). In Denmark, this was also the sense of the word himthige, a variant of húskarl (see below). This meaning can be seen, for instance, on the Turinge stone:

Ketill and Bjôrn, they raised this stone in memory of Þorsteinn, their father; Ônundr in memory of his brother and the housecarls in memory of the just(?) (and) Ketiley in memory of her husbandman. These brothers were the best of men in the land and abroad in the retinue [lid], held their housecarls well. He fell in battle in the east in Garðar (Russia), commander of the retinue [lid], the best of landholders.

According to Omeljan Pritsak, this Þorsteinn may have commanded the retinue of Yaroslav the Wise, the Grand Prince of Kiev. Thus, the housecarls mentioned here would be royal bodyguards; in any case, it can be seen here that the word "housecarl" now applied to a person who fought in the service of a different person.

In Norway, housecarls were members of the king's or another powerful man's hirð. The institution of the hirð in Norway can be traced back to the ninth century. The texts dealing with royal power in medieval Norway, the Heimskringla and the Konungs skuggsjá ("King's Mirror"), make explicit the link between a king or leader and his retainers (housecarls and hirðmenn). There was a special fine for the killing of a king's man, which in Konungs skuggsjá is underlined as an advantage of entering the king's service. Conversely, retainers were expected to avenge their leader if he was killed.