What Every Woman Knows is a 1934 American romantic comedy film directed by Gregory La Cava and starring Helen Hayes, Brian Aherne and Madge Evans.

When they catch poor but ambitious 21-year-old John Shand breaking into their house late at night to use their library, they seize the opportunity.

Impressed by his initiative, they offer him £300 to finance his studies provided that he give Maggie the option of marrying him after five years.

When the influential politician Charles Venables comes to sound him out, Maggie sees him first and takes it upon herself to state that John would resign from the party rather than betray his principles.

Matters finally come to a head on the Shands' second wedding anniversary, with John telling Maggie and her family that he and Lady Sybil are in love.

Things turn out the way she had hoped: John and Lady Sybil's ardor does not survive having to spend an entire month together.