Millions of villagers across the floodplains and deltas of southern Asia rely on shallow tubewells to avoid drinking surface water that is highly contaminated with microbial pathogens. Sadly, the elevated arsenic content of groundwater from many of these wells is frequently leading instead to a slow death from various cancers. This Chapman Conference is intended to review a decade of Earth science research on the mechanism(s) of arsenic mobilization in groundwater of southern Asia, identify those areas where a consensus has emerged and, in the case of several important open questions that remain, determine what types of experiments or studies are needed. Special emphasis will be placed on predicting the likely fate of shallow and deeper aquifers that are currently low in arsenic and therefore offer the most realistic means of remediation in the short to medium term.