Hakkapeliitta (Finnish pl. hakkapeliitat) is a historiographical term used for a Finnish light cavalryman in the service of King Gustavus Adolphus of Sweden during the Thirty Years' War (1618 to 1648). Hakkapeliitta is a 19th-century Finnish modification of a contemporary name given by foreigners in the Holy Roman Empire and variously spelled as Hackapelit, Hackapelite, Hackapell, Haccapelit, or Haccapelite. These terms were based on a Finnish battle cry hakkaa päälle (lit. 'strike upon [them]'; Swedish: hacka på), commonly translated as 'Cut them down!'
The hakkapeliitta-style cavalry was first used during the Polish-Swedish Wars of the late 16th century. In the early 17th century the cavalry led by the Field Marshal Jacob De la Gardie participated in campaigns against Poland and Russia. The Hakkapeliitta cavalry men led by Field Marshal Gustaf Horn were vital to the Swedish victories in Germany during the Thirty Years' War.
The Finnish military march Hakkapeliittain Marssi is named after hakkapeliittas.