South-vergent channel flow from beneath the Tibetan Plateau may have played an important role in forming the Himalaya. The possibility that Greater Himalayan rocks currently exposed in the Himalayan Fold-Thrust Belt flowed at mid-crustal depths before being exhumed is intriguing, and may suggest a natural link between orogenic processes operating under the Tibetan Plateau and in the fold-thrust belt. Conceptual and numeric models for the Himalayan-Tibetan Orogen currently reported in the literature do an admirable job of replicating many of the observable primary geological features and relationships. However, detailed observations from Greater Himalayan rocks exposed in the fold-thrust belt's external klippen, and from Lesser Himalayan rocks in the proximal footwall of the Main Central Thrust, suggest that since Early Miocene time, it may be more appropriate to model the evolution of the fold-thrust belt using the critical taper paradigm. This does not exclude the possibility that channel flow and linked extrusion of Greater Himalayan rocks may have occurred, but it places important boundaries on a permissible time frame during which these processes may have operated. ?? The Geological Society of London 2006.