Fires affect the Earth system in multiple ways. They are a major source of aerosol particles, greenhouse gases, and other trace constituents in the atmosphere (Crutzen and Andreae 1990; Seiler and Crutzen 1980). They alter the exchanges of matter and energy between the land surface and the atmosphere, with important implications for local, regional, and global environmental patterns. Moreover, fires play a significant role in affecting air quality, the ecosystem, land use, public health, and safety. To understand the role of fires in changing climate conditions and socioeconomic landscapes, recent scientific studies of biomass burning have focused on two goals: i) quantifying the emissions of aerosol particles and trace gases from fires and improving the description of spatial and temporal patterns at mesoscale or finer resolutions and ii) characterizing and understanding the effect of these emissions on atmospheric processes at various scales, ranging from human health and air quality impacts at a local scale to cloud properties and precipitation at a regional scale to interactions with Earth’s climate on a decadal scale.