Kaj Birket-Smith (20 January 1893 – 28 October 1977) was a Danish philologist and anthropologist. He specialized in studying the habits and language of the Inuit and Eyak. He was a member of Knud Rasmussen's 1921 Thule expedition. In 1940, he became director of the Ethnographic Department of the National Museum of Denmark.
Kaj Birket-Smith would have been a ripe old age of 128 if he were still alive today.