A compilation and analysis of the size and frequency of the largest known explosive eruptions on Earth are presented. The largest explosive events are defined to be those eruptions yielding greater than 1015kg of products (>150 times the mass of the 1991 eruption of Mt. Pinatubo). This includes all known eruptions with a volcanic explosivity index (VEI) of 8. A total of 47 such events, ranging in age from Ordovician to Pleistocene, are identified, of which 42 eruptions are known from the past 36Ma. A logarithmic magnitude scale of eruption size is applied, based on erupted mass, to these events. On this scale, 46 eruptions >1015kg are defined to be of magnitude M8. There is one M9 event known so far, the Fish Canyon Tuff, with an erupted mass of >1016kg and a magnitude of 9.2. Analysis of this dataset indicates that eruptions of size M8 and larger have occurred with a minimum frequency of 1.4 events/Ma in two pulses over the past 36Ma. On the basis of the activity during the past 13.5Ma, there is at least a 75% probability of a M8 eruption (>1015kg) occurring within the next 1Ma. There is a 1% chance of an eruption of this scale in the next 460–7,200years. While the effect of any individual M8 or larger eruption is considerable, the time-averaged impact (i.e., erupted massfrequency) of the very largest eruptions is small, due to their rarity. The long-term, time-averaged erupted mass flux from magnitude 8 and 9 eruptions is ~10–100 times less than for M7 eruptions; the time-averaged mass eruption rate from M7 eruptions is 9,500kgs–1, whereas for M8 and M9 eruptions it is ~70–1,000kgs–1. Comparison of the energy release by volcanic eruptions with that due to asteroid impacts suggests that on timescales of <100,000years, explosive volcanic eruptions are considerably more frequent than impacts of similar energy yield. This has important implications for understanding the risk of extreme events.