‘Essences’ have had a hard time of it in philosophy over the last forty years; on both sides of the analytic-continental divide, ‘essentialism’ is a dirty word. Yet what if we have no adequate idea of what an essence is? It is one of Deleuze's great virtues that he forces us to think about these questions in new ways, particularly with the theory put forward in his Spinoza books of ‘particular essences’. Since essences are traditionally construed in a more or less Platonic way, as universals or classes which group together individuals in virtue of a set of common characteristics, the notion of a particular essence sounds like a contradiction in terms. In Platonism, according to its received meaning, we have on one side essences (Forms, Ideas or Types), which are universal, unchanging, selfidentical, unitary and eternal, and on the other side we have particular beings, which are changeable, different from themselves, divided into different qualities, and exist in the world of time and space. Platonic essences are fixed and transcendent, real but ideal, abstract and invariant. Deleuze's reading of Spinoza proposes, on the contrary, essences that are mobile and immanent in material things, real and material, concrete and subject to variation. If ‘essentialism’ is belief in Platonic essences – invariant, universal and necessary characteristics that exist somehow independently of the variable particulars these characteristics ‘identify’ as belonging to a certain class or type, and which remain changeless and self-identical through all the changes in contingent states of affairs – or in something that can be seen as issuing from this Platonic notion, then Deleuze's theory of particular essences is in no way essentialist.