Kaj is a given name of unknown origin, particularly common in the Nordic countries, loaned from the Continent. It might be derived from Frisian Kaye (hen) or Latin Caius. In Denmark and Norway, the name is predominantly male, while in Sweden and Finland, the name is unisex (with the female name possibly having a different origin).
Notable persons with the given name include:
Given name
Kaj Arnö (born 1963), Finland-Swedish IT-entrepreneur
Kaj Birket-Smith (1893–1977), Danish philologist and anthropologist
Kaj Birksted (1915–1996), Danish fighter pilot
Kaj Björk (1918–2014), Swedish Social Democratic politician
Kaj Busch (21st century), Australian television presenter
Kaj Christiansen (1921–2008), Danish football forward
Kaj Chydenius (born 1939), Finnish composer
Kaj Czarnecki (1936–2018), Finnish Olympic fencer
Kaj Franck (1911–1989), Finnish designer
Kaj Frederiksen (1916–1991), Danish boxer
Kaj Gnudtzmann (1880–1948), Danish gymnast
Kaj Aksel Hansen (1917–1987), Danish footballer
Kaj Hansen (footballer born 1940) (1940–2009), Danish footballer
Kaj Hasselriis (born 1974), Canadian journalist
Kaj Ikast (1935–2020), Danish politician
Niels Kaj Jerne (1911–1994), Danish immunologist
Kaj Leo Johannesen (born 1964), Prime Minister of the Faroe Islands
Kaj Ulrik Linderstrøm-Lang (1896–1959), Danish scientist
Kaj Munk (1898–1944), Danish playwright
Kaj Poulsen (born 1942), Danish footballer in the striker position
Kaj Ramsteijn (born 1990), Dutch footballer
Kaj Schmidt (born 1926), Danish Olympic sprint canoer who competed in the early 1960s
Kaj Skagen (born 1949), Norwegian writer
Kaj Stenvall (born 1951), Finnish artist
Kaj Aage Gunnar Strand (1907–2000), Danish astronomer
Kaj Sylvan (1923–2020), Danish Olympic sprint canoer who competed in the late 1950s
Kaj Uldaler (1906–1987), Danish amateur football player