The authors combine scholarship from social entrepreneurship and systems literature to identify two dominant pathways used by mission-driven organizations to achieve large-scale social impact. The scaling impact approach expands the reach or depth of a proven solution by unit-level expansion. The impact at scale approach, by contrast, works at a population level to address the problem at scale. Four original case studies illustrate how organizations translate these approaches into strategies to address large-scale social problems. The four strategies are: (1) expanding through scale, (2) expanding through scope, (3) growing through systems optimization, and (4) growing through systems reinvention.