A pdf is available by request from jmheyman@utep.edu . Including a comprehensive summary of environmental issues at the U.S.-Mexico border, this chapter argues that in the main they are caused by the concentration of people and activities around the transaction back and forth of unequal values (e.g., differential wages) in the two adjacent territories of the United State and Mexico. It fits within the unequal exchange tradition of world systems theory but points to the particularly intense concentration of unequal exchange at boundary seams with immediate proximity of unequal spaces/territories.