A central tenet of Reformed theology was the doctrine of justification by imputed righteousness: the faithful are not saved on account of their own righteousness, but purely by the gracious decision of God to ‘impute’ or ‘account’ the perfect righteousness of his Son unto them. While this doctrine was a popular target for broader anti-Calvinist criticism, this chapter demonstrates that Whichcote, Cudworth, More and Smith challenged the Reformed doctrine by producing an explicitly Platonic account of justification on which believers are rendered acceptable to God by deification (i.e. by direct, internal conformity to and participation in the nature of God). This model of justification is distinctive, even against the wider background of English anti-Calvinism, and provides one of the strongest indications of the close philosophical alignment of Whichcote, More, Cudworth and Smith. As the present chapter will demonstrate, to their Calvinist critics such as Anthony Tuckney, it was the Cambridge Platonists’ views about justification that constituted their most egregious departure from Reformed doctrine and that most clearly unmasked the ‘Platonic’ character of their thought.