Oskar Justinus Cohn (21 February 1839 – 6 August 1893), best known by the pen name Oskar Justinus,^[1] was a German playwright and writer.

Oskar Justinus Cohn was born into a Jewish family in Breslau (modern-day Wrocław, Poland). His father, Isaak Cohn, earned a doctorate at an advanced age and for some time held the post of Austro-Hungarian consul.^[1] Among his siblings were biologist Ferdinand Cohn, legal historian Max Conrat [de],^[2] and composer Hugo Conrat [Wikidata].^[3]

Cohn made his debut in the dramatic world in 1861 with his play Der Vereins-Held, which was staged in Breslau.^[4] His literary pursuits came to a pause, however, as he assumed control of the firm established by his father.^[1] He was unsuccessful as a merchant and went into bankruptcy in 1880. Cohn then relocated to Berlin and turned his attention fully to literature, producing several dramatic works in quick succession.

He died in 1893 in Bad Nauheim, where he had sought treatment for a heart condition.^[4]

The writer's 1887 comedy Kyritz-Pyritz was adapted to film in 1930 by Carl Heinz Wolff, as Errant Husbands.