Halfdan ("half Dane") is an Old Norse masculine given name. In Beowulf it is spelled Healfdene, and in Latin sources Haldan. It may refer to:

Mythical figures:

• Halfdan, legendary king of the Scyldings in Beowulf, who also appears in Norse mythology
• Halfdan the Old, ancient legendary king
• Halfdan Hvitbeinn, mythical petty king in Norway
• Halfdan the Valiant (7th century), legendary father of Ivar Vidfamne
• Hálfdan Brönufostri, subject of the legendary saga Hálfdanar saga Brönufóstra
• Halfdan Eysteinsson, subject of the legendary saga Hálfdanar saga Eysteinssonar

People:

• Halfdan (floruit 782–807), Danish client of the Franks
• Halfdan the Black (c. 820 – c. 860), father of Harald I of Norway
• Halfdan Ragnarsson (died 877), Viking, leader of the Great Heathen Army
• Halfdan, possible name of the author of an inscription on a Hagia Sofia parapet
• Halfdan Haraldsson the Black, Norwegian petty king and grandson of Halfdan the Black
• Halfdan, a joint King of Northumbria (reigned 902–910) – see Eowils and Halfdan
• Halfdan the Mild, son of King Eystein Halfdansson, of the House of Yngling
• Halfdan Bryn (1864–1933), Norwegian physician and physical anthropologist
• Halfdan Christensen (1873–1950), Norwegian stage actor and theatre director
• Halfdan Olaus Christophersen (1902–1980), Norwegian historian of ideas, non-fiction writer and World War II resistance member
• Halfdan E (born 1965), Danish film and television composer
• Halfdan Egedius (1877–1899), Norwegian painter and illustrator
• Halfdan Wexel Freihow (born 1959), Norwegian literary critic, novelist, editor and book publisher
• Halfdan Hegtun (1918–2012), Norwegian radio personality, comedian and writer, and politician
• Halfdan Holth (1880–1950), Norwegian veterinarian and professor
• Halfdan Jønsson (1891–1945), Norwegian trade unionist and World War II resistance member
• Halfdan Kjerulf (1815–1868), Norwegian composer
• Halfdan Lehmann (1825–1908), Norwegian government official
• Halfdan T. Mahler (1923–2016), Danish medical doctor and three-term director-general of the World Health Organization
• Halfdan Nielsen, Norwegian speedskater who set the world record in the 10,000 m in 1893
• Halfdan Rasmussen (1915–2002), Danish poet
• Halfdan Strøm (1863–1949), Norwegian painter
• Halfdan Sundt (1873–1951), Norwegian physician and politician