In the decades before and after World War ii, major European department stores were increasingly eager to know and understand their customers. This article analyses how the Dutch department store De Bijenkorf, in dialogue with leading European partners, developed a wide range of research techniques to chart the social composition and buying behavior of its customers in order to enhance the company’s efficiency in procurement, advertising, spatial organization and sales. The customer research of De Bijenkorf helped to legitimize new business policies such as up- and downtrading and impulse buying, but also reflected and established new ideas and images of modern urban consumers as statistical categories behaving in astonishing regular ways. This article is part of the special issue on consumption history and was nominated for the Low Countries History Award in 2019 (for the best article in BMGN - Low Countries Historical Review over the years 2016-2017-2018).