The purpose of this book is to assess, evaluate, and give guidance on the role of elemental speciation and speciation analysis in human health hazard and risk assessment. The book is directed at risk assessors and regulators to emphasize the importance of consideration of speciation in their deliberations. To date, this issue has not been a part of most hazard and risk assessments. Further aims of the publication are to encourage the analysis of speciation of elements to increase knowledge on the effect of speciation on mode of action and to increase understanding of health effects.