Aerosols are small (1 nm-100 µm) and very dynamic particles suspended in the atmosphere. Some of these particles are directly emitted into the atmosphere and others are products of atmospheric synergism. They affect air thermodynamics, climate, ecosystems, agriculture and human health at local, regional and global scale. The net global albedo is increased by atmospheric aerosols counteracting global warming. The climate of cities is strongly determined by these suspended materials. Most aerosols originate from natural sources such as mineral dust, sea spray, volcanoes, natural fi res and biogenic processes. Human activities add dust, soot, sulfates, nitrates and volatile organic compounds (VOCs). Although anthropogenic aerosols are a small fraction (10%) of the global total, their toxicity and concentrations in populated areas make them a hazard to human health. In the Caribbean Region, natural aerosols include the Sahara Air Layer, ash from Le Soufriere volcano in the Lesser Antilles, marine and biogenic sources. Manmade aerosols include PM10, PM2.5, SOx, NOx and VOCs. This chapter will review the assessment of aerosols and their impacts on climate and human health.