This conference is motivated by a desire to bring together the state of social science knowledge on inequality. It will focus both on observation (what is the level of inequality) and on mechanism (what are the likely causes of that inequality). An accurate description of social science knowledge requries distinguishing between dimensions and mechanisms generating inequality that are now understood, versus those for which intellectual controversies exist as well as contexts are are simply not understood. This conference's goal is to carefully lay out what we know and highlight what we do not know, and to do so in a way that can help inform public policy debates.