For Descartes different substances are really distinct. He frequently connects real distinction with mutual separability. I examine this connection and the notion of real distinction. I then apply the results of this analysis to the controversy over the question whether Descartes held that there is a multiplicity of corporeal substances or only one. I argue that there are several ways of defending the pluralist interpretation against the monist charge that Cartesian bodies are not separable and so not really distinct substances.