Wildfires are an integral part of most terrestrial ecosystems. Paleofire records composed of charcoal, soot, and other combustion products deposited in lake and marine sediments, soils, and ice provide a record of the varying importance of fire over time on every continent. This study reviews paleofire research to identify lessons about the nature of fire on Earth and how its past variability is relevant to modern environmental challenges. Four lessons are identified. First, fire is highly sensitive to climate change, and specifically to temperature changes. As long as there is abundant, dry fuel, we can expect that in a warming climate, fires will continue to grow unusually large, severe, and uncontrollable in fire-prone environments. Second, a better understanding of “slow” (interannual to multidecadal) socioecological processes is essential for predicting future wildfire and carbon emissions. Third, current patterns of burning, which are very low in some areas and very high in others—are often unprecedented in the context of the Holocene. Taken together, these insights point to a fourth lesson—that current changes in wildfire dynamics provide an opportunity for paleoecologists to engage the public and help them understand the potential consequences of anthropogenic climate change.