Father Jean Guibert of the Society of St. Sulpice served as superior of the Catholic Institute of Paris. He wrote this short book, which bears an imprimatur, for both those who practice piety and those who disdain it. As noted in the preface to this book, the practice of piety has many advantages. The pious person is drawn into closer contact with God, his heart is purified and made glad, his mind is enlightened, his will is strengthened, and his zeal to love God and neighbor is enkindled. In Part I (Chapters 1-11), Father Guibert discusses the nature of piety, and in Part II (Chapters 12-18), he enumerates its fruits. The sequel to On Piety is Guibert's On the Exercises of Piety, which illustrates how piety is practiced in various ways. (Summary by dave7)