The formulation of Messiaen’s own musical techniques was partly influenced by a variety of established theories. Information about these sources is present in a number of the writings discussed in Chapter 2, but it is the Traité de rythme, de couleur, et d’ornithologie which sheds the most light on Messiaen’s preferred writers and ideas. In order wholly to understand and evaluate the formation of Messiaen’s unique technical language and fully to comprehend its employment in the various stages of his career, it is imperative to examine how he was influenced and borrowed (often quite heavily) from a range of sources. Volumes 1, 4 and 7 of his Traité contain extremely detailed information on the topic; however, there are scant specific details regarding precisely where Messiaen obtained his information. It is the aim of this chapter to clarify and make better sense of Messiaen’s writings on plainchant, Mozart and other theories by examining how they relate to his chosen models.