The Bill and Melinda Gates Foundation has published a new report on Using mobile big data for development. Too often basic information on the poor – who is poor, where do they live and move, how do they manage their social and financial lives? – is scarce, while the costs associated with being underknown are significant. Without formal financial histories, creditworthy individuals cannot access loans when needed most, vaccine workers cannot determine what percent of a region they have immunized from a disease, and relief organizations cannot anticipate where people move when catastrophic events occur. Overall, the quality and efficiency of providing services to the poor suffers.