Lettau (/ˈlɛtaʊ/) is a surname derived from the Old Saxon name for Lithuania. It can be a variant of Lettow, or it may be a habitational name from a former village and lake (also called Littauen) near Waltersdorf in the Mohrungen district of East Prussia's Oberland.
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