Fire is a natural disturbance that occurs in most terrestrial ecosystems. It is also a tool that has been used by humans to manage a wide range of natural ecosystems worldwide. Wildland fire covers a spectrum from low severity, localized prescribed fires, to landscape-level high severity wildfires. The Earth is a fire planet whose terrestrial ecosystems have been modified and impacted by fire since the Carboniferous Period, some 300 to 350 million years before the present time. In the Holocene Epoch of the past 10,000 years, humans have played a major role in fire spread across the planet. Climate change, as well as the burgeoning human population, are now poised to increase the ecosystem impacts of wildland, rangeland, and cropland fire in the 21st Century. Fire can produce a spectrum of effects on soils, water, riparian biota, and wetland components of ecosystems. Fire scientists, land managers, fire suppression, watershed managers, and wildlife personnel need to evaluate fire effects on these ecosystem components, and balance the overall benefits and costs associated with the use of fire in ecosystem management. This publication has been written to provide up-to-date information on fire effects on ecosystem resources that can be used as a basis for planning and implementing fire suppression and management activities. It is a companion publication to the book, Fire’s Effects on Ecosystems by DeBano et al., (1998). This chapter summarizes and provides a synthesis of a recent series of state-of-knowledge general technical reports about fire effects on vegetation, soils, water, wildlife, and other ecosystem resources produced by the USDA Forest Service. The chapter introduces the role of fire severity as the major driver of ecosystem response to fire, and then examines vegetation, soil, water, terrestrial and aquatic biota, air quality, and human cultural impacts of wildland fire.