What Every Woman Knows is a four-act play written by J. M. Barrie. It was first presented by impresario Charles Frohman at the Duke of York's Theatre in London on 3 September 1908. It ran for 384 performances, transferring to the Hicks Theatre between 21 December 1908 and 15 February 1909. The play was first produced in America, also by Frohman, in 1908 at Atlantic City on 18 October 1908, transferring to Broadway, at the Empire Theatre in New York City in December 1908. The production starred Maude Adams and Richard Bennett. Written before women's suffrage, the play posits that "every woman knows" she is the invisible power responsible for the successes of the men in her life.

Sir James Matthew Barrie, 1st Baronet, (9 May 1860 - 19 June 1937) was a Scottish author and dramatist, best remembered today as the creator of Peter Pan. The child of a family of small-town weavers, he was educated in Scotland. He moved to London, where he developed a career as a novelist and playwright. There he met the Llewelyn Davies boys who inspired him in writing about a baby boy who has magical adventures in Kensington Gardens (included in The Little White Bird), then to write Peter Pan, or The Boy Who Wouldn't Grow Up, a "fairy play" about this ageless boy and an ordinary girl named Wendy who have adventures in the fantasy setting of Neverland. This play quickly overshadowed his previous work and although he continued to write successfully, it became his best-known work, credited with popularising the name Wendy, which was very uncommon previously. Barrie unofficially adopted the Davies boys following the deaths of their parents. Barrie was made a baronet by George V in 1913, and a member of the Order of Merit in 1922. Before his death, he gave the rights to the Peter Pan works to London's Great Ormond Street Hospital, which continues to benefit from them.