Synopsis The geology of Assam is ultimately the product of an ancient landmass caught up in the collision zones of three other landmasses. These were originally its neighbours, but drifted apart with the break-up of the Gondwanaland. Later, they collided again to produce the present geological and continental framework. The geology is therefore very complex, and, in order to provide the reader with a reasonably clear picture, we have had to go into the overall geological processes that have affected not only the State of Assam, but also its surrounding lands. We have had further to integrate the geology with the many elements of Plate Tectonics, which have led to the formation of all the mountain belts and sedimentary basins in this area.