This paper is an attempt to identify the source of Deleuzian thought, that is, the "plane" or "image" from which it unfolds despite its many twists and turns. This, I believe, is immanence. The thread of immanence appears most clearly in What Is Philosophy? but can be shown to have been at work from the very start. But immanence is not just the plane of Deleuzian thought. It is also, and above all, that of philosophy itself, especially in its difference from religion and onto-theology. This in turn means that, following Spinoza and his univocal ontology, Deleuzian thought can be seen as completing or realizing the conditions of philosophy itself.