The Boston Exposure Assessment in Microenvironments (BEAM) study was designed to examine the concentration distributions of VOCs in various microenvironments in and around Boston with the main objective of reducing the uncertainties in predicting exposure levels. A suite of VOC's with potential health effects including benzene, toluene, ethylbenzene, xylenes, several chlorinated compounds and aldehydes were collected in all microenvironments. Phase I. BEAM examined common non-residential microenvironments that have not been extensively studied, in particular, dining, shopping, and transportation microenvironments. Sampling using scripted activities in these microenvironments. For some compounds, levels in stores were several times higher than those found in transportation microenvironments, indicating strong indoor sources. Using data from BEAM microenvironments and the literature, a stochastic population exposure model was developed to determine the contribution of these microenvironments to total personal exposure for four cohorts - employed males/females, and unemployed males/females. Overall, female non-workers had the largest contribution to exposure from the dining and shopping microenvironments, while male workers had the lowest. The median contribution to total personal exposure ranged from less than 1% for several compounds to 8% for styrene. At the 95th percentile, these two microenvironments could contribute from 10% to 70% of a person's exposure, depending on the compound. Further analyses include comparisons of worker exposure in office, shopping, and dining jobs. Phase II. We examined the effect of and variability within residential microenvironments as well as the contribution of workplace to personal exposure. For this phase, personal, home indoor and outdoor, and workplace samples were collected from 55 participants across two seasons. The contribution of secondary source areas such as basements, attached garages, and common apartment hallways were estimated. The median percent of air flow to zone 1 (the residential zone) from the basement was 14% in the summer and 48% in the winter. The median percent of air flow in zone 1 from the common apartment hallway was 10% across both seasons. The percent contribution of the basement to zone 1 concentrations varied across compounds and seasons with medians ranging from 0 to 32%. For the hallway, the medians were lower, ranging from 0 to 13%. Attached garages are also impacting the indoors; those homes with attached garages had significantly higher concentrations of BTEX compounds than those homes without. Future analyses include indoor source rate estimates and personal exposure modeling.