Recent philosophers assess differently the extent to which affinity is to be found between the idealist metaphysics of G. W. Leibniz and George Berkeley. I argue that these figures’ idealisms are indeed strongly aligned. They espouse related accounts of the nature of mental substance and state. They similarly restrict the domain of causality. They each reject the Lockean primary/secondary quality dichotomy. Over against the criticism that idealisms cannot allow for a distinction to be made out between real and illusory perceptual experience, the two philosophers offer comparable solutions. Nevertheless, their ontologies are not identical, and are primarily to be distinguished in terms of their disparate characterisations of ultimate reality as being either immanent or transcendent to percipient subjects like us. This continuum of transcendentism and immanentism has further application as a conceptual tool both for tracing the rise of modern philosophy and for developing new metaphysical and epistemological accounts of the nature of the world and our relation to it.