The natural environment plays a critical role in offsetting the anthropogenic carbon emissions. Despite the size of the global groundwater store the processes controlling the concentration and characteristics of organic matter in groundwater are poorly understood. Through a survey of global carbon concentrations, it is apparent that groundwater carbon concentrations are significantly lower than terrestrial (soil, sediment and river) concentrations. This indicates that terrestrial OM is biologically processed (and a potential source of inorganic carbon) or sorbed to mineral surfaces (a sink of carbon). This will be explored through an ARC Discovery research project which will investigate factors that determine groundwater organic matter concentration, how important is groundwater to the terrestrial carbon budget and under what conditions where groundwater is a carbon source or sink. This project is bringing together geochemists, ecologists, hydrologists and anyone with an interest in organic matter in groundwater. Specifically, the amount of colloid and dissolved organic matter present will be quantified, the rate and extent of biological processing, desorption and sorption will be investigated and the relative importance of each process to be determined. The processes that control organic matter in groundwater will be investigated at a range of field sites with differing surface soil, land cover, recharge type and hydrological properties. Preliminary results from various field sites has shown that sedimentary organic matter is mobilised as water flows through the hyporheic zone. The results from this project will provide guidelines for the management of groundwater resource as part of the carbon economy.