Units are the foundation for all measurement of the natural world, and from which standard, our understanding develops. This book, stemming from a conference on the history of units organised by the editors, provides a comprehensive and discursive introduction to the history of units within physics, in advance of the proposed redefinition of the SI base units at the General Conference on Weights and Measures in 2018. Precise Dimensions: A history of units from 1791-2018 features contributions from leading researchers in metrology and history, and will be of particular interest to historians of science, as well as to scientists with an interest in the history of the units they work with.