It is easy in a work such as this, which focuses on the human work of evangelization, to lose sight of the fact that evangelization is a work of grace. The Holy Spirit evangelizes through the word of God. Grace builds on nature, but it is more than nature. Much of what follows touches on very human factors, but evangelization does not consist only in applying human resources. Even were this book free from error and full of insight, it would still be a partial and very imperfect discussion of the process of evangelization. Rich sources for understanding its spiritual and specifically supernatural aspects are the papal statements on the subject, beginning with On Evangelization by Pope Paul VI published on Dec. 8, 1975. Popes since then have frequently returned to the theme. The Apostolic Exhortation The Joy of the Gospel (Evangelii gaudium) by Pope Francis merits special attention.