Susan Horowitz Cain (born 1968) is an American writer and lecturer.
She is the author of the 2012 non-fiction book Quiet: The Power of Introverts in a World That Can't Stop Talking, which argues that modern Western culture misunderstands and undervalues the traits and capabilities of introverted people. In 2015, she co-founded Quiet Revolution, a mission-based company with initiatives in the areas of children (parenting and education), lifestyle, and the workplace. Her 2016 follow-on book, Quiet Power: The Secret Strengths of Introverts, focused on introverted children and teens, the book also being directed to their educators and parents.
Her book Bittersweet: How Sorrow and Longing Make Us Whole (2022) focused on accepting feelings of sorrow and longing as inspiration to experience sublime emotions—such as beauty and wonder and transcendence—to counterbalance the "normative sunshine" of society's pressure to constantly be positive.