Ernst Åke Kromnow (2 May 1914 – 27 April 1986) was a Swedish archivist, historian and civil servant.

He was secretary in the Swedish National Union of Students from 1937 to 1939 and he received a Bachelor of Arts degree the same year.

[1] During World War II, Kromnow was part of the Swedish intelligence agency C-byrån.

He was board member of the Delegation for Military History Research (Delegationen för militärhistorisk forskning) 1966–1982, Archive of the Swedish labour movement (Arbetarrörelsens arkiv) 1966–1982, Swedish Emigrant Institute in Växjö 1966–1979, Board of the Nordic Museum 1967–1984 (vice chairman in 1970), Skansen 1967–1984.

Kromnow was chairman of the State Archives Board (Statens arkivstyrelse) 1977–1979, Association of Swedish Cultural History (Föreningen för svensk kulturhistoria) 1977–1984 and vice chairman of the government agency National Art Museums (Statens konstmuseer) from 1979.