"Shifting Sands: Unsound Science and Unsafe Regulation" examines how irreproducible science affects select areas of government policy and regulation governed by different federal agencies. This first report on "PM[subscript 2.5] Regulation" focuses on irreproducible research in the field of environmental epidemiology, which informs the U.S. Environmental Protection Agency's (EPA) policies and regulations. It focuses upon scientific research that associates airborne fine particulate matter smaller than 2.5 microns in diameter (PM[subscript 2.5]) with mortality, heart attacks, and asthma. [Introduction by Peter W. Wood.]