The DSH’s rock formations appear to have experienced distinct periods of deformation, producing a variety of fold types. Repeated thrusting and piling up of nappes occurred during successive folding phases due to tight isoclinal to recumbent folds with substantial mass transfer in a north–south orientation. Pioneer geologists explained the general structure of the rocks in the Darjeeling Group, which exposed rocks from Neogene Siwalik and Late Palaeozoic Gondwana-equivalent rocks in the south through the Proterozoic Daling sequence and the crystalline gneissic complex of the Darjeeling Group passing through Kanchenjunga-Lamo Angdang to Palaeozoic-Mesozoic Trans-Axial/Tethyan sequences of Sikkim-Tibet border in the north. The tectonic geology of the DSH is characterized by a recurring feature: the younger up-dip towards the south, which is mostly attributed to thrusting and recumbent folding, as suggested by Indian geologists. This chapter primarily focuses on providing a succinct but comprehensive overview of the DSH’s major geological structure and tectonics features.