This chapter introduces Edumetrics as a data-driven framework for measuring human capital in the twenty-first century, inspired by Lord Kelvin’s principle that improvement begins with measurement. Positioned at the intersection of economics, education and the social sciences, it argues that quantifying learning outcomes is not only possible but essential to scientific progress and sound policy. The book situates edumetrics within the tradition of human capital theory while emphasizing its interdisciplinary scope and methodological innovations. By harmonizing international learning assessments since 1970, edumetrics makes it possible to trace long-term trends in both quality and equity worldwide, revealing their economic implications. Ultimately, it reframes the education–growth nexus by shifting the focus from schooling years to actual skills, offering new evidence for the design of more effective and equitable policies.