Otto Julius Bierbaum (28 June 1865 – 1 February 1910) was a German writer.

Composers such as Pauline Volkstein set his texts to music.

In 1897 Bierbaum published his novel Stilpe which inspired Ernst von Wolzogen to establish, in 1901, the first cabaret venue ever in Berlin, the Überbrettl .

His novel Zäpfel Kerns Abenteuer was an adaptation of Carlo Collodi's Pinocchio.

Bierbaum's final novel, Yankeedoodlefahrt, was published in 1909 and is the source of the adage "Humor ist, wenn man trotzdem lacht" ("Humor is when you laugh anyway"), which has become a proverb in modern German.