Halfdan the Mild (Old Norse: Hálfdan hinn mildi) or Halfdan the Meek was the son of king Eystein Halfdansson, of the House of Yngling and he succeeded his father as king, according to Heimskringla. He was king of Romerike and Vestfold.

He was said to be generous in gold but to starve his men with food. He was a great warrior who often pillaged and gathered great booty.

His wife was Liv, the daughter of king Dag of Vestmar. Halfdan the Mild died of illness in his bed.
He was succeeded by his son, Gudrød the Hunter.