An article about genre classification of early modern British books published in Transformations: A DARIAH Journal, 1(1), 2025. Abstract below:This article introduces an open-box workflow for labelling 94 percent of the English Short Title Catalogue (ESTC) with a unified genre classification scheme, as well as an approach to evaluating the classifications. As the ESTC covers most of the surviving books published in the early modern Anglosphere, our categorisation offers new opportunities for large-scale quantitative research on the early modern book trade. Our evaluation process directly engages with the ambiguity of any genre labelling or annotation schemes of early modern books and highlights problematic boundaries between the categories. We also provide summary statistics about the genre composition of the ESTC, demonstrate how the new data can be used to detect biases in other datasets of early modern books and discuss further possibilities for genre-related computational work with the ESTC.