Ignimbrites are vast, landscape-modifying deposits composed mainly of pumice fragments and ash. They derive from the most hazardous types of explosive volcanic eruptions and record rapid sedimentation from catastrophic pyroclastic density currents that sweep across the ground. Since early work on ignimbrites by P. Marshall (1935), H. Kuno (1941), R. L. Smith (1960) and R. V. Fisher (1966), there has been a dramatic increase in research into these enigmatic deposits. Particularly instructive field studies include those of ignimbrites from the large caldera volcanoes of the western USA, from the arc volcanoes of the Mediterranean region, Japan, Southeast Asia, South America and New Zealand, and from intraplate volcanoes such as the Canary Islands. Experimental-analogue and numerical modelling of pyroclastic density current behaviour and sedimentation have recently complemented the field-based work. Now there is a bewildering plethora of ignimbrite classification schemes, emplacement models and deposit interpretations. It is therefore timely to take stock, to synthesize modern understanding, and, in particular, to consider how field investigations of ignimbrite lithofacies can best be used both to infer actual pyroclastic density current behaviour and to constrain or test the various models. A fresh look at ignimbrite _ emplacement is all the more important with the recognition that ignimbrites can relate to eruptions with magnitudes sufficient to impact global climate and biota.