Compared with conventional methods that are used to investigate polluted sites and soils, treebased methods in which trees act as bio-indicators or proxy recorders of current and past pollution are significantly less costly, can be implemented rapidly and with minimum equipment, have minimal environmental effects, and can be used even in areas that are difficult to access (urban areas or topography). Samples collected from trees can represent a mixture of water collected from multiple depths and soil gases. Therefore, tree samples can represent a much larger sampling zone than a typical monitoring well. The presence of contaminants within a tree can be used to gain information on subsurface contamination. Although these methods, called phytoscreening and dendrochemistry, were known to only a few scientific experts worldwide in the early 2000s, this research program was established to further test the methods on well-documented sites and on new contaminants and to communicate relevant information to render the methods accessible to users.