This chapter recovers a more controversial and politically engaged image of Cambridge Platonism, makes a case for their inclusion more centrally in the history of the English Revolution and its aftermath. It explores the question of their possible radicalism, in the context of the interrogation of radicalism. The chapter argues that there are aspects of Cambridge Platonism which deserve to be termed radical in the same sense as John Milton, even if one might want to set a limit to their radicalism in other respects. As their eighteenth-century legacy implies, far from being backward-looking, the Cambridge Platonists were at the forefront of developments in contemporary thought in their time. The Cambridge Platonists were every bit as radical as Milton in their emphasis on free will, and Milton every bit as learned as they in his theology. Among indicators of religious radicalism, heterodox Trinitarianism and, especially, denial of the doctrine of the Trinity, are hugely important.