The Exposure Factors Handbook provides information on various physiological and behavioral factors commonly used in assessing exposure to environmental chemicals. The handbook was first published in 1989 and was updated in 1997. Since then, new data have become available. This updated edition incorporates data available since 1997 up to July 2011. It also reflects the revisions made to the Child-Specific Exposure Factors Handbook, which was updated and published in 2008. This edition of the handbook supersedes the information presented in the 2008 Child-Specific Exposure Factors Handbook. Each chapter in the 2011 edition of the Exposure Factors Handbook presents recommended values for the exposure factors covered in the chapter as well as a discussion of the underlying data used in developing the recommendations. These recommended values are based solely on NCEAs interpretations of the available data. In many situations, different values may be appropriate to use in consideration of policy, precedent, or other factors.