© 2015, Springer-Verlag London. The rapid economic development occurring in developing countries in recent decades has been accompanied with increasingly worsened air quality. In recent years, severe air pollution episodes have occurred frequently in the cities of some developing countries. The goal of this chapter is to describe outdoor air pollution issues with a focus on urban areas in developing countries. Topics include global air pollution trends, differences in emissions and concentrations of key air pollutants in different regions, emission sources disproportionately affecting developing countries, estimating disease burden in developing countries, and recommendations based on historical successes and lessons from developed countries.