Jahn (Jähn) is a German surname. Notable people with this surname include the following:

• Constanze Jahn (born 1963), German chess player
• David Jahn (born 1975), Czech burlesque impresario
• Eduard Jahn (1871–1942), German mycologist and microbiologist
• Erich Jahn (born 1907, date of death unknown), Hitler Youth leader
• Friedrich Ludwig Jahn (1778–1852), German educator, founding figure of German Turner athletic movement
• Gunnar Jahn (1883–1971), Norwegian politician and resistance member
• Gunter Jahn (1910–1992), German U-boat commander
• Hans Max Jahn (1853–1906), German physical chemist
• Helmut Jahn (1940–2021), German-American architect
• Hermann Arthur Jahn (1907–1979), British scientist
• Jan Jahn (1739–1802), Czech painter and art historian
• Jeff Jahn (born 1970), American artist and critic
• Johann Jahn (1750–1816), German Orientalist
• Kurt Jahn (1892–1966), German general
• Marie-Luise Jahn (1918–2010), German physician
• Martin Jahn (c. 1620 – c. 1682), German church musician, minister, hymnwriter
• Martin Jahn (born 1970), Czech economist and politician
• Joseph Michael Jahn (born 1943), American author and critic
• Molly Jahn, American plant scientist and food security policy advisor
• Otto Jahn (1813–1869), German archaeologist, philologist, and writer on art and music
• Patrick Jahn (born 1983), German football player
• Robert G. Jahn (1930–2017), American scientist, electrical engineer, and psychic investigator
• Ryan David Jahn (born 1979), American novelist and screenwriter
• Sigmund Jähn (1937–2019), German astronaut
• Thomas Jahn (born 1965), German film and television director
• Wilhelm Jahn (1835–1900), Austro-Hungarian orchestral conductor
• Willie Jahn (1889–1973), German athlete, leader of the Wandervogel youth movement, folksong composer, publisher, World War II army officer