1,4-Dioxane (dioxane) is a probable carcinogen that has received increased attention in recent years, largely due to improved analytical methods that can detect it at lower concentrations.  There is no Federal Maximum Contaminant Level for dioxane, however in 2008, the USEPA included dioxane on its Contaminant Candidate List.  Also this year, several states in the Northeast increased regulatory requirements for dioxane.  Regulatory requirements in the Northeast states are reviewed.  Existing information on dioxane’s properties, uses, analysis, and remediation are also reviewed.  Dioxane’s physical and chemical properties include high water solubility, low tendency to adsorb, and low volatility.  These properties make dioxane difficult to analyze because dioxane will not readily leave the water phase.  Recently developed modifications of analytical methods (usually 8260 or 8270) must be employed to detect dioxane at the low concentrations that are often of concern.  Dioxane has been used in a variety of processes and products, but it was mainly used as a solvent stabilizer for 1,1,1-trichloroethane (TCA).  Because of its higher boiling point, dioxane tends to become concentrated in vapor degreasing wastes.  Other properties of dioxane are very different from those of TCA, which has implications for fate and transport and remediation.  Dioxane is more mobile, therefore plumes can be much larger than accompanying TCA plumes.  Remediation technologies that may work well for TCA may not work well for dioxane, and often a treatment train is necessary to treat all the contaminants of concern.  Granular activated carbon is typically ineffective for dioxane remediation, as are air stripping, air sparging, and zero-valent iron walls.  Although dioxane is thought to be relatively resistant to biodegradation, bioreactors have been used to treat dioxane at several sites.  Chemical oxidation technologies, especially employing ozone with hydrogen peroxide or ultraviolet light with hydrogen peroxide, have proven to be effective for dioxane remediation.