John Goodwin (1594-1665) is said by his biographers to have converted from Calvinism to Arminianism, in a matter of months, in the year 1647. Thereafter Goodwin went on to write several Arminian works, including Redemption Redeemed in 1651. In this dissertation it is argued that his conversion was neither as rapid nor radical as has been argued hitherto. Progressively and with increasing clarity of expression he rejected the hypothetical universalism imbibed during his formative years, particularly what he perceived to be its deterministic component. ‘Calvinism’ is a misnomer for what he rejected. His theological development, discernible from a diachronic consideration of his earliest extant sermons and writings from the 1630s and early 1640s, was towards a soteriology wherein God’s grace and a man’s free will work concurrently, but wherein every stage of a man’s conversion and perseverance is ultimately determined by man himself. His theological trajectory, therefore, was away from something akin to hypothetical universalism and towards this principle of humanly determined concurrence. The dissertation focusses on the doctrine of perseverance in particular, and considers the array of discrete arguments that Goodwin makes in Redemption Redeemed for the possibility of total and final apostasy by true believers. It is shown that the whole panoply is consistent with and underpinned by this humanly determined concurrence principle. The analysis of these arguments is then used to make a systematic comparison with some important prior Arminian works on perseverance, in order to draw conclusions concerning his contribution to the advancement of the Arminian cause. John Owen (1616-83) responded to Goodwin’s work by publishing The Doctrine of the Saints’ Perseverance in 1654. From the context and content of Owen’s response to Goodwin’s arguments, it is shown that Owen’s arguments reflect a divinely determined concurrence principle. He teaches that God’s grace is effectual in every stage of a man’s conversion and perseverance, such that God is the ultimate arbiter of man’s destiny; but that his grace never operates in such a way as to compel a man to believe or persevere against his will. This analysis is then used to make comparisons with Goodwin’s work, and with influential prior Reformed works on perseverance, from which conclusions are drawn concerning Owen’s distinctive contribution to the perseverance doctrine. By comparing Goodwin’s position and Owen’s in terms of these two underlying principles, it is shown that there is a material difference between the anti-Arminian case that Goodwin proceeds to rebut and the anti-Arminian case that is in fact made by Owen. In important respects, Goodwin’s argument does not engage with the position contended for by Owen and the antecedent authors whose works are considered herein. While this does not necessarily detract from the internal logical coherence of Goodwin’s positive case, it does expose a lacuna in his negative case as expressed in Redemption Redeemed. It is a lacuna that undermines the claim that it was ‘Calvinism’ that Goodwin rejected, or even ‘destroyed’, as some have suggested – at least in so far as the term ‘Calvinism’ is understood as referring to the theology of Owen. Either because Owen wrote second, or because he had well understood the Arminian case from Goodwin and his antecedents, there is not a corresponding dramatic lacuna in Owen’s anti-Arminian case.