Abstract: Tectonically, the Greater Mekong subregion is the southward or southwestward extension of the Nujiang-Lancangjiang-Jinshajiang tectonic zone in southwestern China and the Caledonian fold zone in southern China. On the basis of the findings of the extension trends of individual tectonic units and their interrelations, the tectonic units in this region have recently been divided into four first-order tectonic units including the Indo-Australian plate, Sino-Burma-Malaysia block, Indo-China block and South China block, bounded by the Indo-Burma Ranges, Lancangjiang-Bentong-Raub and Jinshajiang-Ailaoshan-Song Ma suture zones. Moreover the Sino-Burma-Malaysia and Indo-China blocks may be separately subdivided into four second-order tectonic units, i.e. the Western Burma, Tengchong-Moulmein, Baoshan-Shan Thai and Lincang-Kengtung microblocks within the Sino-Burma-Malaysia block, and Jinghong-Phrae-Eastern Malaysia, Simao-Da Lat, Kon Tum and Truong Son microblocks within the Indo-China block, bounded by the secondary suture zones. The South China block is separated into the Yangtze and Cathaysia microblocks by the Chay River suture zone in northern Viet Nam. The Hoh Xil-Lancangjiang-Bentong-Raub suture zone is interpreted as the boundary between southern Gondwana Land and northern Laurasia Land. The Kon Tum and Truong Son microblocks are believed to be the southwestward extension of the Cathysia microblock, and the equivalent west of it may be the Qamdo microblock.