Robin Gwynn has, by his own admission, spent half a century investigating the impact of the Huguenots on late Stuart Britain. This has resulted in three substantial volumes. The first two (published in 2015 and 2018) concentrated on the numbers and institutional resilience of those who fled the persecutions of Protestants in Louis xiv's France; this last volume argues for the impact these people had – especially in ensuring the success of the revolution of 1689, and in allowing William iii to hold his own in his war with the French that began in that year. Throughout this project, Gwynn has argued that the scale and significance of the Huguenot migration has been underplayed and underestimated by most scholars, and his case in this volume rests on three main planks. First, he suggests that the arrival of large numbers of fleeing French Protestants, especially from 1687, created the political conditions in which English people could unite around the idea of regime change, and in acceptance of William and Mary as their new monarch. The refugees brought tales of suffering at the hands of a Catholic regime, and their plight seemed a vivid illustration of the possible fate of the whole European Reformation: and the effects were disastrous for James ii. The political atmosphere in England was soured just as the monarch was advancing policies which would benefit adherents of the Roman faith, and was doing so using the sort of claims for unstoppable monarchical power (and with the same disregard of earlier promises) that seemed to mark Louis xiv's approach to religion. James's subjects noted both the parallels, and their ruler's lack of sympathy for the Huguenots, and this fed just enough resentment that they – at the very least – sat on their hands when William's Dutch forces invaded the realm in the autumn of 1688. Gwynn's second argument for the significance of French refugees comes in the military sphere. He suggests that Ireland was crucial to the war against France in 1689–91 and, in particular, that the new London regime's first response to the rebellion against its authority by Irish Catholics, and its victory at the battle of Aughrim in 1691, avoided it getting hopelessly bogged down in its western kingdom. Huguenots, Gwynn maintains, were crucial to both successes. He provides a vindication of William's commander in Ireland in 1689, the French Protestant Frederick Herman von Schomberg. Schomberg has been criticised by some commentators for delay and caution in his campaign; but this book suggests that he acted decisively to land his troops in Ulster, that he was key in pressing relief of the siege of Derry (a crucial early triumph) and that he was not responsible for the failure of the Williamite forces to advance beyond Dundalk over the winter of 1689–90. Gwynn also lauds the courage and success of the Huguenot troops serving at Aughrim. Without them, this close-run success would not have been secured, and the Irish war would have been extended for at least another twelve months. Thirdly, this work shows how central French Protestants were in gathering money for the war. Building on the work of other scholars on the ‘financial revolution’ (that series of changes in the mechanisms for paying for government that marked the 1690s, and which centred on the creation of a long-term funded public debt, largely managed by the newly-founded Bank of England), Gwynn posits that William's survival against the French would have been impossible without Huguenot input. The French Protestant community in London were key supporters of the Bank: they subscribed capital to it in large amounts (15 per cent of its original fundraising), and those who had been in England for some decades (French people had been fleeing an increasingly intolerant Bourbon regime for some time), served in disproportionate numbers as its early directors. All these cases are backed by door-stop appendices, which the author generously hopes will help future research, and may end up being its most important contribution to scholarship. One lists the identifiable Huguenot officers serving in Stuart forces in the later Stuart period; one catalogues the elders and deacons of the French church in London (with a good deal of biographical information on each figure to demonstrate their imbrication in English national life); one – fascinatingly – is able to list some rank-and-file Huguenot soldiers, using a record of the recipients of charity after the disbandment of regiments in 1699. All of this is a valuable contribution, and this reviewer has only a few quibbles: especially in the face of the huge effort involved in gathering the information on which the argument of the book is based. It is true that Huguenots can be overlooked in surveys of late Stuart history, and that this work will be a useful corrective; but the historiographic targets can sometimes feel a bit dated. The work most in the firing line, by Warren Scoville, was published in 1960; and there has been quite a bit work this current century that has stressed the continued purchase of confessional divisions in Europe to the end of the seventeenth century, and the role of Huguenot networks and experience in maintaining Protestant identities and commitments. More of this might have been acknowledged. To take a solipsistic example, it is true that this reviewer's 1996 work on William iii's propaganda said too little on the topics covered in Gwynn's volumes, but my 2007 review of ideas of the Protestant international in English thought from 1660 to 1760 argued that Louis's persecutions were absolutely central to England's self-perception and to people's thoughts about their nation's place in the world. In places too, Gwynn's work veers towards a ‘must have’ style of arguing. It is almost certainly true that English people were appalled by Louis xiv's persecution of non-Catholics, and were more ready to accept William iii as a replacement for James ii as a consequence – but one might have hoped for more explicit evidence that folks actually thought this way. Their impressive generosity in giving to efforts for charitable relief is suggestive, but is, in the end, circumstantial. Also, the work has a wide diversity of focus – from individuals such as Schomberg, to political reactions to mass forced migration in the late 1680s, to the economic behaviour of a community that had been established in London for decades before that. This raises slight doubts about how far this is a history of a coherent phenomenon. However, one could argue that the range of Huguenot impacts is a crucial finding of this work: and, in truth, this reviewer's objections are minor. Taken together, the material in this work makes a cogent case that the Huguenot experience should be taken seriously; and perhaps that religious ideology should be taken more seriously for this period too. In the end, Huguenots mobilised English support because they were committed Protestants. They fought for William because they were committed Protestants; and they lent him money (despite the precariousness of new financial expedients) for that same reason.