There is a growing recognition of the need to identify when exposures to specific combinations of chemicals result in toxicological effects of concern. In order to meet this need new tools are required to evaluate the doses of multiple chemicals that occur from the concurrent exposures to multiple sources of the chemicals. Limitations associated with the traditional approach for exposure modeling (source-to-dose models) have led to the development of a new approach that focuses on the person. These Person Oriented Models (POMs) use available data on personal characteristics that are statistically representative of the population receiving an exposure. Once the person's characteristics are defined, the information is used to model the probability of being exposed during a particular period of time. This process is repeated for different time periods and for hundreds or thousands of persons to produce a description of longitudinal exposures across a population. This approach allows the modeling of route-specific doses from multiple concurrent exposures; allows the modeling of doses from time varying exposures across, individuals, and provides a basis for modeling the person-related characteristics in subsequent steps in the process of assessing risks from mixtures.