Numerous epidemiological studies show a positive association between ambient PM2.5 concentrations and adverse health effects. However, many exposure studies found poor correlations between ambient PM2.5 and personal exposure. In epidemiological studies, central-site PM is used as a surrogate for exposure to outdoor PM. Few investigations have been performed to evaluate how accurate and precise that assumption is for community exposure. Moreover, people spend a large majority of their time indoors, leading to additional concerns about the health effects of particles generated indoors, or the contribution of outdoor particles to indoor environments. To address these issues, the Relationship of Indoor, Outdoor and Personal Air (RIOPA) study was designed to investigate indoor, outdoor and personal exposures to several classes of air pollutants, including VOCs, aldehydes and PM2.5. Samples were collected from summer, 1999 to spring, 2001 in Houston (TX), Los Angeles (CA), and Elizabeth (NJ). Indoor, outdoor and personal PM2.5 samples were collected in 212 non-smoking residences, 162 of which were sampled twice. Some homes were chosen due to close proximity to ambient sources of one or more target analytes, while others were farther from sources. Results from this study will be presented, including: the contributions of outdoor and indoor sources to indoor concentrations quantified using a single compartment box model with measured air exchange rate and a random component superposition (RCS) statistical model, source apportionment performed using positive matrix factorization (PMF), and regressions performed to elucidate significant factors affecting indoor air quality.