A major theme of the European Enlightenment was the rationalization of value, the use of reason to determine the value of things, from diamonds to civilizations. This view of the Enlightenment is well-established in the human sciences. It is ripe for extension to the natural sciences, given the rich recent literature on affect, evaluation, and subjectivity in early modern science. Meanwhile, in art history, the new history of connoisseurship provides a model for the historical study of the evaluation of material things. Historians of natural history have already noted the connections between science, Enlightenment, and connoisseurship. The time has come to extend their insights to other areas of Enlightenment science. This means recognizing the breadth of connoisseurship – the social, linguistic, and disciplinary diversity of the practice – as understood in Europe in the eighteenth century and the latter part of the seventeenth century. An outline of the three papers in this special section gives an indication of how this historiographical project might be carried out.