From the beginning of history, measurement has been interwoven into the human experience, shaping our understanding of nature, personal relationships, and the supernatural. We measure the world to know our past, comprehend the present, and plan the future. Renowned physicist Piero Martin explores how scientific knowledge is built around seven key pillars of measurement: the meter for length; the second for time; the kilogram for mass; the kelvin for temperature; the ampere for electricity; the mole for quantity of substance; and the candela for luminous intensity. Martin examines the history and function of these units and illustrates their applications in rich vignettes on a range of topics—from quarks to black holes, from a glass of wine to space exploration. He delves into not only the all-important numbers but also anecdotes that underline each unit's special quality. At the same time, he explains how each unit contributes to important aspects of science, from classical physics to quantum mechanics, from relativity to chemistry, from cosmology to elementary particle physics, and from medicine to modern technology. Martin eloquently shows how the entire universe can be measured and understood using just seven units.