Drawing on perspectives from several academic traditions, we argue that sustainability is best understood as intergenerational social equity. When viewed thusly, it is possible to determine what socially responsible organizations look like in practice. After reviewing historic claims and evidence of sustainability, we turn to modern applications of institutionally based sustainability. We then describe sustainability in the framework of an intergenerational social equity model, claiming that the legacies of social and cultural institutions are evidence of sustainability in action. We conclude with a discussion of what it means for an organization to be socially responsible given our understanding of sustainability.