Half the Sky: Turning Oppression into Opportunity for Women Worldwide is a nonfiction book by husband and wife team Nicholas Kristof and Sheryl WuDunn, published by Knopf in September 2009. It is also a 2012 PBS documentary based on the book. The book argues that the oppression of women worldwide is "the paramount moral challenge" of the present era, much as the fight against slavery was in the past. The title comes from a famous Mao Zedong quote "women hold up half the sky", although the authors cite it only as a "Chinese proverb".