Environmental pollutants are receiving increasing attention in the news media and in scientific publications because of their widespread occurrence and their potential harmful effects to humans and other organisms. Almost every day we see new reports about environmental problems such as arsenic pollution in drinking water in Bangladesh and in mine tailings in the Sierra Nevada foothills of California, lead in house paints, and plutonium and uranium in soils near nuclear materials processing plants. A new field referred to as Molecular Environmental Science has developed over the past few years to address these types of problems. Two of the key pieces of information needed to assess the potential danger of environmental pollutants are their chemical speciation at the molecular level and how they react with the surfaces of natural solids, which can sequester pollutant species or transform them to less toxic forms. Synchrotron x-ray absorption spectroscopy (XAS) can provide this information for a wide range of heavy metal and metalloid pollutants in complex environmental samples. Examples of synchrotron-based XAS studies of a number of environmental pollutants will be discussed and used to illustrate some of the important environmental issues faced by modern society.