Fire is an important cross-cutting process in the Earth System. It is a significant determinant of vegetation dynamics, biogeochemical cycling, and atmospheric chemistry at global, regional and landscape scales. It also impacts on nutrient fluxes, surface albedo and cloud development. Earth observation and paleoclimate data plus direct observations have shown that fire regimes (burnt area, fire intensity etc) have dramatically changed in many parts of the world (especially the boreal, humid tropical and Mediterranean biomes), with often negative impacts on vegetation cover, soils, hydrology, carbon sinks and emissions to the atmosphere and so on. In many regions, fire is an important and highly variable source of air pollutant emissions, and it thus constitutes a significant factor, controlling inter-annual variability of the atmospheric composition. Given the multitude of potentially important interactions and feedbacks, it is vital that fire should feature as an integral part of Earth System Models. Work in this area is progressing but is still relatively nascent. It is supported by increasingly available observations of fire impacts, fire activity, burnt areas, and various species in the atmospheric smoke plumes. In recent years, satellite-based instruments measuring these aspects of fire have become increasingly more accurate.