Current global discussions over the content of the post-2015 sustainable development agenda provide a critical space for reflection on the future contours of development assistance, and an opportunity to rethink the social dimensions of the transformation to sustainable development. There is widespread recognition that the future agenda must be ambitious, universal and transformative; with policies and implementation mechanisms that are integrated, holistic and measurable. This article explores some of the challenges of moving from the poverty-focused targets of the MDGs, towards a socially sustainable development agenda, and points to directions that could help shape a fundamental rethinking of the current approach to social development.