Lettau (/ˈlɛtaʊ/) is a surname of East Prussian origin derived from the Old Saxon name for Lithuania. Lettow is its Pomeranian variant. Until the end of the Second World War, Lettau was the name of a village and adjacent lake in the Oberland (highlands) of Upper Prussia southeast of the Bay of Danzig.
People with the surname include:
- Andre Lettau, German live midstakes poker player
- Georg Lettau (1878–1951), German lichenologist
- Heinz Lettau (1909–2005), professor of meteorology at the University of Wisconsin
- Kevyn Lettau (born 1959), American jazz vocalist
- Reinhard Lettau (1929–1996), German-American writer and professor