I propose in this text a rhythmic theory of signs drawn from the thought of Gilles Deleuze and Félix Guattari. I name this theory a semiorhythmology. I suggest that the theory of rhythm developed in A Thousand Plateaus (1980) can be understood, in part, as the culmination of the diverse set of inquiries into signs that both Deleuze and Guattari undertook, individually and together, beginning in the 1960s. I first outline Deleuze’s theory of signs as a theory of encounter as developed in Proust and Signs (1964) and Difference and Repetition (1968), following which I sketch Guattari’s engagements with signs and semiotics throughout the 1960s and 1970s, particularly through his notion of “a-signifying semiotics” and the concept of the “diagram” he adapts from the semiotics of Charles Sanders Peirce. I close by showing how these heterogeneous theories of the sign are drawn together in A Thousand Plateaus through the Spinozist reading of the ethology of Jakob von Uexküll and the theorisation of rhythm in the form of the refrain.