An ice stream is a part of an inland ice sheet that flows rapidly through the surrounding ice. The distinction between an ice sheet and an outlet glacier is clear in principle but muddy in practice-many Antarctic glaciers are intermediate in character. The ''Ross ice streams,'' which flow through the West Antarctic inland ice into the Ross Ice Shelf, are distinct in character, differing even from other ice streams in the marine ice sheet of West Antarctica. Their surface elevation profiles are low, their bed slopes are low and smooth, and their driving stresses diminish monotonically downglacier. In transverse profile they are boarder in relation to ice thickness and exhibit shallower subglacial trought, than other ice streams. Many models for the fast sliding of glaciers have been applied to the Ross ice streams; most have included in some form a reduction in basal drag resulting from a lesser effective than glaciostatic pressure at the bed. Most models are only semiphysical at best, so need to be ''tuned'' by fitting to assumed parameters at some place or places in the real ice sheet. The recent discovery of a very small effective pressure beneath one ice stream consequently has led to some gross errors in the velocities predicted by the models. The difficulty may be resolved if it is true, as recent experiments suggest, that ice stream B, and by extrapolation other Ross ice streams as well, slide on a deforming bed that absorbs most or all of the differential motion between the ice and the bedrock. ¿ American Geophysical Union 1987