_Scale-Up in Education, Volume 1: Ideas in Principle_ examines the challenges of "scaling up" from a multidisciplinary perspective. It brings together contributions from disciplines that routinely take promising innovations to scale, including medicine, business, engineering, computing, and education. Together the contributors explore appropriate methods for estimating the effects of innovations in larger, more diverse settings and provide theories and models to guide the design of innovations most likely to remain viable at large scales. Specially-commissioned commentaries also discuss the analytical requirements and theoretical possibilities of a program of educational research on scale-up built upon these foundations. This volume is ideally suited for researchers, policymakers, and graduate students charged with determining the effectiveness of educational interventions. With its insights into the conceptual and methodological prerequisites for obtaining rigorous, actionable evidence of intervention effects, the volume provides reading for program evaluation courses in schools of education and public policy.