Chapter 5 examines taxonomic practices of merchants and other users of money to better understand how early modern coins worked in circulation. After-death inventories offer insights into people’s domestic taxonomies, that is, into practices of classifying, labelling, and compartmentalising the money that people encountered as they went about their lives. Mercantile and institutional account books show how people linked different currencies. Assayers’ conclusions, derived from testing tiny specks of matter, were disseminated widely in broadsheets, coin tariffs, and conversion tables, but also in privately collated notes and letters. This information allowed early modern people to relate coins to one another and to convert them into monies of account which were much more homogeneous. This work was more than merely coping with chaos. People’s ability to match coins with transaction types and geography marked out circuits for specific currencies. The spaces in which currencies like the Dutch guilder could circulate freely thus emerged from the ground up. Users’ taxonomic practices were just as crucial for upholding monetary order as the knowledge work performed by assayers, minters, and government officials.