This is the first biography of Joseph McCabe (1867-1955), a former Catholic preist who became one of the best-known champions and a prolific popularizer of freethought and rationalism in the first half of the 20th century. McCabe's encyclopedic curiosity, rigorous scholarship, and above all his unswerving intellectual honesty led him through a tumultuous career of public lecturing and debating, and an incredible output of over 200 books. He tackled the most controversial issues of the modern era: evolution, biblical errancy, belief in God, immorality, spiritualism, capitalism vs. socialism, women's rights, and many other topics. Much of his writing was published in the form of the "Little Blue Books" by E. Haldeman-Julius, who declared McCabe to be "the world's greatest scholar." Today in our postmodern period, where Enlightenment values are being questioned and irrationalism in many guises has become fashionable, McCabe's gift for rational inquiry, respect for scientific evidence, and lucid, no-nonsense prose are both relevant and welcome.