People living in poverty suffer from an increased burden of illness. The increase in respiratory illnesses in poor populations spans a spectrum from immuno-preventive respiratory infections in refugee populations to tuberculosis among the inner-city homeless. Such populations suffer from greater exposures to disease-causing agents and from depressed host resistance to those microbes. This article discusses the latter cause. Studies are reviewed that show the associations between poverty and respiratory disease; between poverty and such factors as stress, poor nutrition, low birth weight, and co-infections; and those associations that help dissect the pathogenic pathways by which these factors impair host defenses against infection. In the end, such influences are aggregate, and the conditions of poverty and the growing inequality in resource distribution emerges worldwide as a major determinant of health.