Fire has always been an important component of many ecosystems, but anthropogenic global climate change is now altering fire regimes over much of Earth's land surface, spurring a more urgent need to understand the physical, biological, and chemical processes associated with fire as well as its effects on human societies. In 2020 AGU launched a Special Collection that spanned 10 journals, soliciting papers under the theme "Fire in the Earth System" to encourage state-of-the-art publications in fire-related science. The completed Special Collection comprises more than 100 papers. Here we summarize the articles published in this collection, considering them to be grouped into seven themes: paleofire and its ties to climate; evolution of fire patterns in the recent past and the future, including the effects of ongoing climate change; physical (atmospheric) and chemical processes associated with fire; ecosystem effects, including on biogeochemical cycles; physical landscape change after fire and its associated hazards; fire effects on water quality, air quality, and human health; and new methods and technologies applied to fire research.