Early in the twentieth century, the industrialist Andrew Carnegie established the Carnegie Foundation for the Advancement of Teaching to create a pension system for the nation's college professors. The introduction of this pension system proved an ingenious educational reform. At the time, American higher education was a largely ill-defined enterprise with the differences between high school and colleges often unclear. To qualify for participation in the Carnegie pension system, higher education institutions were required to adopt a set of basic standards around courses of instruction, facilities, staffing, and admissions criteria. The Carnegie Unit, also known as the credit hour, became the basic unit of measurement both for determining students' readiness for college and their progress through an acceptable program of study. Over time, the Carnegie Unit became the building block of modern American education, serving as the foundation for everything from daily school schedules to graduation requirements, faculty workloads, and eligibility for federal financial aid. Today, the Carnegie Unit is under intensifying critique from educators and education policymakers who want to make student performance more transparent and the delivery of education more flexible. They see the Carnegie Unit as a significant impediment to the changes they seek. They advocate for innovations that support transparency and flexibility, including competency-based education models. In an effort to inform these reform conversations and serve a constructive catalyst for change, the Carnegie Foundation launched a study to revisit the role, function, and uses of the Carnegie Unit. They explored in detail the nature of the problems that reformers aim to address and the complexity of the systems in which these problems are embedded. They analyzed what a shift away from the Carnegie Unit toward a competency-based (rather than an instructional time-based) metric might entail for the operation of educational institutions and the students they serve. Finally, they considered the scope of innovations necessary to replace the Carnegie Unit, the ambitiousness and uncertainties associated with these tasks, and the vast array of practical problems that would need to be solved. The study's findings and the Carnegie Foundation's recommendations are presented herein. Appended are: (1) Improvement Science Principals; (2) Carnegie Foundation for the Advancement of Teaching Board of Trustees; and (3) Carnegie Unit Advisory Committee. A bibliography is included.