Systems of units still fail to attract the philosophical attention they deserve but this could change with the current reform of the International System of Units. This book invites a philosophical inquiry that promises to overcome the tensions that have long obstructed science studies.

Nadine de Courtenay is Associate Professor of History and Philosophy of Science at the Paris Diderot University & Laboratoire SPHERE, France.

Olivier Darrigol is Research Director at CNRS & Laboratoire SPHERE, France.

Oliver Schlaudt is Associate Professor of Philosophy of Science at Heidelberg University, Germany.

1. Introduction; 2. The origins of the Metre Convention, the SI and the development of modern metrology; 3. Justifying and motivating an SI for all people for all time; 4. Reforming the International System of Units: On our way to redefine the base units solely from fundamental constants and beyond; 5. Strategies for the definition of a system of units; 6. Relations between units and relations between quantities; 7. On the Conceptual Nature of the Physical Constants; 8. And how experiments Begin: The International Prototype Kilogram and the Planck Constant; 9. The SI and the Problem of Spatiotemporal Constancy