The characteristics, distribution, and formation mechanisms of large resurgent calderas (RC) are surveyed. Definitive features include large diameter (in the tens of km), the upheaval of the center of the caldera floor (in the hundreds of meters), and the presence of large thicknesses of welded ignimbrite resulting from massive pyroclastic flows during RC-forming eruptions. The use of Landsat and Skylab images, confirmed by field studies, was needed to identify two Andean RCs camouflaged by their very size. RCs are found to be rare (no more than 10 in the last million years), and they are shown to occur in different geological settings sharing the characteristic of a thick crust melted away or penetrated by a rising basaltic magma driven by a strong thermal plume. The stages of RC formation are described: precaldera doming, caldera collapse, eruption of air-fall material and pyroclastic flows, postcaldera resurgence, and late lava flows. The catastrophic effects a RC-type eruption would have on human activity, primarily due to the fall of centimeter-thick layers of co-ignimbrite ash over several million sq km, are balanced against the mineral and geothermal-energy resources associated with extant RCs.