Hans Henny Jahnn (17 December 1894, Stellingen – 29 November 1959, Hamburg) was a German playwright, novelist, and organ-builder.
As a playwright, he wrote: Pastor Ephraim Magnus (1917), which The Cambridge Guide to Theatre describes as a nihilistic, Expressionist play "stuffed with perversities and sado-masochistic motifs"; Coronation of Richard III (1922; "equally lurid"); and a version of Medea (1926). Later works include the novel Perrudja, an unfinished trilogy of novels River without Banks (Fluss ohne Ufer), the drama Thomas Chatterton (1955; staged by Gustaf Gründgens in 1956), and the novella The Night of Lead. Erwin Piscator staged Jahnn's The Dusty Rainbow (Der staubige Regenbogen) in 1961.
Jahnn was also a music publisher, focusing on 17th-century organ music. He was a contemporary of organ-builder Rudolf von Beckerath.
He met Gottlieb Friedrich Harms, with whom he was united in a "mystical wedding" in 1913, at a secondary school (the St. Pauli Realschule) which they both attended, and they lived together between 1914 and 1918. They met Ellinor Philips in 1918. In 1919, Jahnn founded the community of Ugrino with a sculptor, Franz Buse. In 1926, Jahnn married Ellinor, and Harms married Sybille Philips, Ellinor's sister, in 1928.
Jahnn's bisexuality, well-documented in his life, appears as well throughout his literary work.