Debates around quality versus quantity in education can generate controversy about how quality is measured. Many question the drive to delineate and quantify precisely what works, suggesting that much value either cannot be measured or is distorted by measurement. This book explores how we can understand measurement in areas of education policy, planning, and practice that have not previously been considered measurable. The contributors ask four main questions: What do we measure and not measure when we try to measure the unmeasurable in education? When attempts have been made to measure the unmeasurable in education, what metrics have been adopted in which contexts, and with what outcomes? Why have measures been adopted as indicators of the unmeasurable, such as human rights? And how have particular organisations approached the problem of measuring the apparently unmeasurable in education, with what epistemological, normative, and conceptual resources, and consequences? The book draws on analyses from philosophy, history, sociology, and economics, with insights from national and international contexts. The contributions consider philosophical distinctions, historical experiences, and contemporary reflections on how to refine existing approaches to measurement of poverty, capability, rights, and the benefits of education. The discussion shows how measuring the unmeasurable takes account of the inequalities, complexities and uncertainties of work in education, thus suggesting a considerable deepening of the notion of education quality and measurement. This book was originally published as a special issue of Comparative Education.