The Teesta River originates in the Tibet Himalayas and flows through the Indian States of Sikkim and West Bengal before entering Bangladesh, where it flows into the Brahmaputra. This international River is considered to be the lifeline of Sikkim and northern part of West Bengal. The Teesta valley is rich in biodiversity and variegated vegetation, and the river provides various livelihoods for the residents along its entire length of 414 km. The river has a mention in the ancient history and changed its course a number of time as a result of flooding. It remained in the centre of conflict over allocation of its water with the neighbouring nation and also for the hydro electricity power projects posing threat to the river communities as it flows through the earthquake-prone, ecologically and geologically fragile region. The author, a school teacher in Coochbehar, has a close affinity with the river since his young ages and this book is the result of his long standing research work, the best effort covering the course, the history, the geography, various projects and challenges of the river.