A New York Times Critics' Best Book of 2018 An Economist Best Book of 2018 A Spectator Best Book of 2018 A Mental Floss Best Book of 2018 An unprecedented history of the personality test conceived a century ago by a mother and her daughter--fiction writers with no formal training in psychology--and how it insinuated itself into our boardrooms, classrooms, and beyond The Myers-Briggs Type Indicator is the most popular personality test in the world. It is used regularly by Fortune 500 companies, universities, hospitals, churches, and the military. Its language of personality types--extraversion and introversion, sensing and intuiting, thinking and feeling, judging and perceiving--has inspired television shows, online dating platforms, and Buzzfeed quizzes. Yet despite the test's widespread adoption, experts in the field of psychometric testing, a $2 billion industry, have struggled to validate its results--no less account for its success. How did Myers-Briggs, a homegrown multiple choice questionnaire, infiltrate our workplaces, our relationships, our Internet, our lives? First conceived in the 1920s by the mother-daughter team of Katherine Briggs and Isabel Briggs Myers, a pair of devoted homemakers, novelists, and amateur psychoanalysts, Myers-Briggs was designed to bring the gospel of Carl Jung to the masses. But it would take on a life entirely its own, reaching from the smoke-filled boardrooms of mid-century New York to Berkeley, California,