Healthy communities focus on the complex interactions of the social and environmental factors that determine health at a macro level. This requires studying not only the effects of biological, chemical, and physical agents but also socioeconomic factors, including housing, urban development, land use, transportation, industry, and agriculture. Specific research areas may include: outdoor air quality, surface and recreational water quality, human exposure to industrial or agricultural waste streams, the psychosocial environment, community stressors, and environmental justice and tribal issues.