Orthodoxy (1908) is a book by G. K. Chesterton that has become a classic of Christian apologetics. Chesterton considered this book a companion to his other work, Heretics. In the book's preface Chesterton states the purpose is to "attempt an explanation, not of whether the Christian faith can be believed, but of how he personally has come to believe it." In it, Chesterton presents an original view of Christian religion. He sees it as the answer to natural human needs, the "answer to a riddle" in his own words, and not simply as an arbitrary truth received from somewhere outside the boundaries of human experience.
The book was written when Chesterton was an Anglican. He converted to Catholicism 14 years later. The title, Orthodoxy, is meant to avoid such sectarian questions.