It is now four decades since Geoffrey Cantor, reviewing the Porter and Rousseau collection of 1981 entitled The Ferment of Knowledge, observed that the eighteenth century is for historians of science a “problem”, and indeed a multiple problem: the period had long been a “grey area on the historical chart”, with no plausible “master narrative” and no Newton or Faraday to supply any landmarks; it was largely overlooked in general histories of science; and more recently historians had tended to “set up simplistic, monolithic interpretations” of it. The purpose of this special issue is to draw renewed attention to that cluster of problems and to offer some solutions. Because the problem is multiple, the solutions are multiple as well. Some of the contributions reconsider traditional, yet surprisingly persistent, interpretations of the eighteenth century: both Emma Spary and Domenico Bertoloni Meli engage with “Enlightenment” (focusing respectively on re-enchantment and on Hankins’ textbook), while Brendan Dooley uses natural history in early eighteenth-century Padua to shed new light on such themes as deism and social reform. In contrast, Anita Guerrini offers a new perspective on what is perhaps the main recent growth area of eighteenth-century historiography, namely collecting, while Richard Sorrenson’s article identifies improvement as a major theme that has often been overlooked by historians of science. Finally, Adrian Wilson treats the eighteenth-century development of natural knowledge as a whole, depicting this as the realisation of Bacon’s vision of a “Great Instauration”. All these contributions draw on the wider lessons of The Ferment of Knowledge and of Cantor’s review essay. Those lessons include the value of thinking about scientific change in terms of the evolution of the map of knowledge; the need to take historiography seriously; and above all, the value of being explicit about the master narratives that we are working with, whether our aim is to question the old ones, create new ones, or synthesise those we already have.