Messiaen’s music is rhythmically and harmonically complex. It reflects, as he affirmed, the miraculous beauty of God’s Creation. By the early 1940s, he had developed a musical language of religious symbolism comprising a variety of components. The building blocks on which this language is based and the contents their inventor intended them to represent were clearly defined, and hardly changed in the course of the composer’s long life. This article gives an overview of this symbolism and discusses the prevalent devices Messiaen used, along with the religious concepts informing each of them.