Hálfdanar saga Eysteinssonar is a legendary saga from early 14th century Iceland about Halfdan Eysteinsson. The main events appear to take place in the 9th century.
Halfdan's grandfather was Þrándr, the eponymous king of Trondheim, who in turn was the son of Sæmingr, king of Hålogaland and son of Odin. Sæmingr had married Naumu who had given her name to Namdalen. Þrándr had married Dagmær, the sister of Svanhvít, the heroine of Hrómundar saga Gripssonar, and they had had the sons Eysteinn and Eirikr inn víðförli. Eirikr is the hero of Eireks saga víðförla and discovered Ódáinsakr. Eysteinn married Ása, the daughter of Sigurd Hart, and Áslaug, the daughter of Sigurd Snake-in-the-Eye. They had several sons, of whom Halfdan was one.
It deals with Eysteinn's adventures in Staraja Ladoga (Aldeigjuborg), his conquest of Alaborg, and the adventures of his son Halfdan.