Halfdan Bryn (20 May 1864 – 5 March 1933) was a Norwegian physician and physical anthropologist.
Bryn was born in Trondheim, Norway, the son of physician Thomas Bryn (1813–1902) and Kristine Emilie Karoline Richter (1826–1869). He was a grandson of Thomas Bryn, Sr., and a brother of Knud Ørn Bryn and Alfred Jørgen Bryn. In November 1892, he married Wilhelmine "Willa" Thane (1873–1929). He was also an uncle of Alf Bonnevie Bryn and Finn Bryn.
Bryn took his examen artium in 1882 and graduated cand.med. from the University of Oslo in 1889.
Bryn first practiced as a physician in Dakota and New York between 1890 and 1891, before working as a chief resident at the hospital in Trondheim from 1891 to 1892, and then starting his own medical practice. However, he was conscripted as an army doctor, at first with the rank of lieutenant. He served at first as a military doctor in Trondheim, from 1894 holding the rank of captain. He was head of the Decorative Line Company from 1901 to 1904 and of the land conservation partnership from 1904 to 1907. In 1911, he was appointed brigade major and from 1916 was medical physician to the 5th Brigade, remaining in this position until 1924, when he was discharged from the military.
As an army doctor, Bryn had good opportunities to study men from different parts of the country. His work with military recruits inspired him to do research on physical anthropology. Recognizing his interest, Colonel Hans Daae made it possible for him to conduct studies in the field, sometimes almost on a full-time basis. In 1914, he published his first anthropological work, Anthropological surveys I, and in 1917, he won the King Haakon VII gold medal for another work. That same year he received a scholarship from the Nansen Fund for conducting anthropological studies in Norway.