Summary The risk assessment approach described in this monograph applies only to essential trace elements (ETEs) involved in human health and not to non-essential elements. The purpose of this monograph is to provide the scientific principles that support the concept of an "acceptable range of oral intake" (AROI), which uses a "homeostatic model" for determining the range of dietary intakes for essential trace elements (ETEs) that meet the nutritional requirements of a healthy population and avoid excess intakes. To facilitate comparisons, AROIs are discussed in relation to other risk assessment approaches. Although it includes examples, this monograph is not a compendium of assessments on ETEs, nor is it a textbook detailing the scientific basis of risk assessment of the derivation of dietary reference intakes.