Scholars often depict the early modern period as a moment of movement, connectivity, and boundary crossing. Within the histories of science, medicine, and technology, however, an emphasis on “specific circumstances and close, local settings”—in other words, locality—persists in the production of certain kinds of knowledge (2). By foregrounding cinchona, or Peruvian bark—one of the leading remedies and commodities of its day—A Singular Remedy suggests that both local and transoceanic processes contributed to a shared body of medical understandings, therapeutic practices, and imaginaries related to the bark’s consumption in this age of commerce.A tree bark harvested from South America’s mountain forests, cinchona is now recognized to contain alkaloids (quinine among them) that interfere with malaria plasmodia in human red blood cells. Although they did not understand it in such terms at the time, Andean healers had used the bark for its febrifugal properties long before it entered the European medical ken by the 1680s. The next several centuries witnessed a growing awareness of the bark’s ability to treat intermittent fevers and attempts to steal, transplant, and grow the trees from which it came. Given the long-distance commodity chains involved in its trade, cinchona remained expensive and difficult to identify with certainty, though the mass migrations, forced and free, of the early modern world ensured a steady supply of potential patients for remedies that could treat tropical diseases. Cinchona, or one of its many substitutes, thus became an essential component of health care among big, transoceanic institutions like the armed forces or the slave trade. In other words, as Gänger ably shows, cinchona became a tool of empire building, notably in Africa and Asia during the nineteenth century, as well as during the eighteenth across the Atlantic world, through a process that reshaped knowledge about the bark.The idea that knowledge could be movable, contingent, and compatible with the relevance of locality both reflects and advances recent scholarship about early modern medicines and long-distance trade, supporting an analytical move toward identifying material things at the heart of ways of seeing and understanding the world.Though the bitter, medicinal bark takes pride of place in its title, A Singular Remedy is not just a global history of cinchona. Gänger uses the bark’s spread from 1750 to 1820 to argue for movement and commerce as generative, rather than erosive, of science. From Lima to Luanda and Japan to Paris, individuals prepared, consumed, traded, and worried about cinchona, producing novel and common views of the bark and its effects. Such a scope and scale, covering an impressive array of sources and languages, enables Gänger to push against two principal historiographical trends associated with cinchona—its positivist links to quinine and, by extension, its association with life-saving innovation within the British Empire. In so doing, A Singular Remedy transcends the limits of the national or imperial frameworks that often organize early modern history, especially many previous histories of cinchona, to offer an account of how bark knowledge was shared between and across the Atlantic empires.The concept of empire is inescapable throughout A Singular Remedy. It functions less as a reference to science’s imperial ties than a lens to present matters of ecology, economy, unfreedom, labor, and warfare in service to Gänger’s methodological emphasis on contingency, idiosyncrasy, and mutability in cinchona’s history. Within the book’s history of medicine framework, this contingency means recognizing that observers today cannot say for certain that cinchona “cured men and women in the past, nor that it even afforded them relief” despite the eventual identification of its pharmacological properties (19). What remains for readers are the stories about, and understandings of, the bark transmitted along infrastructures instituted and maintained by empire.Chapters demonstrate an attention to evidence, approaches, and vocabularies from numerous historical fields, including cultural, economic, environmental, and intellectual history, in addition to the histories of science, medicine, and technology. Using these tools, the book traverses a busy Atlantic world (and beyond)—what Gänger calls cinchona’s “many elsewheres,” populated by administrators, merchants, soldiers, slaves, sufferers, healers, and laborers—in tracing cinchona’s origin stories, production, distribution, use, and the consequences thereof (26). Evocative details of sweetened febrifugal lemonades or the conversion of bark export figures into quantities of doses underscore the human element of the story amid the sheer amount of information conveyed. Gänger also is sensitive to issues of human difference and indigeneity within the scientific and medical discourses most central to the study. The wealth of detail and references reflect the ambitious scope and scale of A Singular Remedy, though breadth sometimes precludes narrative depth.By interweaving records of cinchona from across a vast geography and chronology, crossing literal and figurative boundaries along the way, Gänger has constructed a valuable resource for those examining early modern trade, empire, medicine, and ideas from a range of methods or disciplines. Though systems and structures occupy key roles in the analysis, cinchona’s particular physical characteristics also shaped those larger processes, as the book’s title suggests. The question arises whether the bark was a singular case or an exemplar of the commodification and circulation characteristic of the long eighteenth century. Given the success of the approach in A Singular Remedy, the lessons deserve to be applied elsewhere.