The authors present an exhaustive catalogue of desmids of the Eastern Himalaya, including most parts of Sikkim and the northern regions of West Bengal (Kalimpong, Lava, Lolegaon etc.). In spite of an enormous range of biodiversity very little work has been done on algal diversity particularly of desmids of the Eastern Himalaya region, which is considered one of the key global biodiversity hotspots. Since Turners (1892) groundbreaking "The freshwater algae (principally Desmidieae) of East India", there has been no monographic account of the desmids of India and neighbouring countries. On the basis of 1000 algal samples collected from almost all accessible localities and habitats of these regions, 272 taxa under 27 genera of desmids are described and illustrated. Out of 272 taxa 25 members under 7 genera include Saccoderm desmids and 247 members under 20 genera belong to Placoderms. 34 taxa under 4 genera (Actinotaenium, Closterium, Cosmarium and Micrasterias) are described as new to science. In addition one new combination under Cosmarium [C. cohnii (Nobilis) Keshri et Das] is proposed here. 6 genera (Ancylonema, Genicularia, Roya, Teilingia, Triplastrum and Triploceras) are new additions to the desmid flora of Eastern Himalaya. 78 taxa under 17 genera are new additions to Indian desmid flora, and 152 taxa are new additions to Eastern Himalayan desmid flora. An updated account of the work done by earlier workers is given in the review section. Detailed methodology and easy identification keys to the taxa level have been provided along with distinct camera lucida drawings and supporting microphotographs. Since no up-to-date record of desmids was available for this part of the globe, this volume will help researchers, environmentalists and amateurs of Eastern Himalayan and Asian countries to identify and study this interesting group of microalgae.