Blau may refer to:
- blue in German and Catalan (cp. Tramvia Blau, a blue streetcar line in Barcelona)
- Blau (Danube), a tributary of
- As a surname
- Amram Blau, an Israeli Naturei-Karta rabbi
- Dick Blau (born 1943), a Professor of Film at the University of Wisconsin-Milwaukee
- Karl Blau, a musician based in Anacortes, Washington
- Lajos Biró (born Blau), (1880–1948), Hungarian novelist, playwright, and screenwriter
- Ludwig Blau, Hungarian scholar and publicist
- Marietta Blau (1894–1970), Austrian physicist
- Raphael Blau (1912-1996), American screenwriter
- Peter Blau (1918–2002), Austrian Jewish sociologist
- Yosef Blau, Orthodox rabbi
- Herbert Blau (born 1926), director and theoretician of performance