Understanding and characterizing risks to children has been the focus of considerable research efforts at the U.S. Environmental Protection Agency (EPA). Potential health risks resulting from environmental exposures before conception and during pre- and postnatal development are often difficult to recognize and assess because of a potential time lag between the relevant periods of exposure during development and associated outcomes that may be expressed at later lifestages. Recognizing this challenge, a lifestage approach for assessing exposure and risk is presented in the recent EPA report titled A Framework for Assessing Health Risks of Environmental Exposures to Children (U.S. EPA, 2006). This EPA report emphasizes the need to account for the potential exposures to environmental agents during all stages of development, and consideration of the relevant adverse health outcomes that may occur as a result of such exposures. It identifies lifestage-specific issues associated with exposure characterization for regulatory risk assessment, summarizes the lifestage-specific approach to exposure characterization presented in the Framework, and discusses emerging research needs for exposure characterization in the larger public-health context. This lifestage approach for characterizing children's exposures to environmental contaminants ensures a more complete evaluation of the potential for vulnerability and exposure of sensitive populations throughout the life cycle.